tennis player continous quitter
Why are chess players quitters?

How many blowout basketball games have you watched where both sides basically throw in the JV bench-warmers because the outcome of the game is not in doubt. In fact, this happens in all sorts of timed team sports. Isn't this analogous to resignation?
Chess has a set of attributes that lend it to resignation:
1. There comes a point at which the outcome of the game is no longer in doubt.
2. There is no personal pride to be found in finishing the game, or other reason to finish the game despite losing, such as improving statistics or beating a personal best time.
3. Because chess is more personally interactive it is even considered an insult to refuse to resign because the winning procedure is so elementary.
Imagine if a professional tennis player had outplayed his opponent so badly that all he needed to do at that point was to land enough serves within the service box to win, because his opponent's "position" was that hopeless that he could not even hit a return. That scenario doesn't happen in tennis, but if it did, it would be polite among high-level tennis players to resign in such a losing position.

and to the OP: this is an interesting question, so thanks. The question "why resign?" is very frequently asked here as rhetorical question, but I've never seen it asked as a genuine question. It's more interesting than I thought.

I don't want to delve too deeply into this discussion, as I think the question asked is absurd; that is, there are some situations where resigning is so natural that to even propose such a question is an insult to our intelligence. Furthermore, I'd like to note that these types of questions seldom come from high-rated players, which should tell you something about their nature.
With that out of the way, I'd like to point something out that everyone here seems to have missed. In virtually all physical sports, people watch not only for the result, but also for the physicality of the players. I can attest to this, as I've recently explored American football, and my primary reason for watching is just to see the crazy athletics at play.
In chess, there are indeed many mental gymnastics which make the "sport" fascinating to watch. However, when a player is "busted" (where most serious players resign), there is nothing of substance left to watch. Likewise, there is nothing of substance left to play. Even if the player can miraculously win, there is nothing interesting here; only some massive mistake by the opponent or another form of oversight (maybe clock management).
In a race, one gets the sense of a runner overcoming all odds to come out on top by expressing true physicality; i.e. their physical genius. In fact, the only way you'd come back from such a deficit is if you run faster than you've ever ran before. In chess, if a player draws a Q & K vs K ending, it's just a disappointment for all involved. Nothing exciting, nothing to be learned, and 99.99% of the time nothing to be gained. Conversely, you can save time and play another game or just rest your head by resigning.

The original post concerning atheletes of other sports missed a critical aspect of continuing in a lost position. Player statistics and placement in a race even if you wern't in the top three finishers is important. In chess there are only 3 statistics that are important win-loss-draw and the ratios between each. If your position is bad why continue in the hope that your opponent makes a mistake. In a Swiss pairing tournament first round high rated players aginst the lower, does the lower rated player realistically have a chance to win? Unless the higher player gets sloppy I don't think the lower has much of a chance. Second round game the lower rated player drops down again due to the difference in ratings. By the third round the lower rated player should be reasonable close in pairings so has a reasonable chance to win. If a one day tournament the 4 game possibilities depend upon the # of attendees & their rating. 2 day tournamnets often draw a larger crowd improving the odds for a lower rated player.
Online chess your rating is less about skill and more about # of games played. If you can keep your game frequency high enough your rating will come up to a plateau.
Another aspect that makes chess different is when have you actually won the game. Many times the endgame is nothing more than clean up. Often the seeds of the win or loss are sown in the first 15 moves.
The race analogy is wrong.
A racer completing the race is to a chess player completing a swiss tournament, even though the prizes are gone.
Resigning in a chess game is closer to a racer breaking his or her leg during the race and quitting, because there's absolutely no way for him or her to win.
Finishing a race has some pride, some "win" to it. Moving your king around and watching your opponent promote 3 queens is pointless and a waste of time, given your opponent is not stalemate-prone.
It's not so in other sports. In football you can be loosing 0-5 but still enjoying the game and trying to make it 1-5 at least. In running competition you can be last runner but still fighting the clock and even making a personal best result.
Also, your example in high level chess is wrong as well.
High level players in serious games do care about the result, but they also care a lot about the quality of their games. Playing a clearly lost position with a 0.01% chance of coming back (opponent gets a heart attack or touches a piece by accident) is playing the lottery, and just shameful and an insult to their opponent's intelligence.
Can you imagine two master level players in a classical tournament, where one master literally has to checkmate his opponent with a queen + king vs king? Ridiculous.
There is no quality/practice to be gained anymore, unlike in sports.
"Furthermore, I'd like to note that these types of questions seldom come from high-rated players, which should tell you something about their nature."
Are you familiar with groupthink? Or the global financial crisis? Lots of experts can sometimes all do something unthinkingly just because that's what everyone else is doing. I can list endless examples of this. Actually this idea that we shouldn't question "experts" is the single biggest problem in the world.
I think the culture should change and games should be played out longer -- at least until the endgame. Even top players will sometimes make mistakes. Why give up and quit if you still have a 5% chance of winning or drawing through less than perfect play by your opponent or some other occurrance?

Chess is different from sports because when you are losing a game of soccer/football, you aren't given a handicap in your attempt to come back. As has been already stated (and a perfect explanation, not sure why it's not good enough for you), the equivalent would be if every time the other team scored a goal, one of your teammates was forced to sit out until such a point as you were losing by 10 goals and it was 1v11.
What is the point of continuing? If anything, this make believe cultural expectation of yours is to continue even when losing. But it's not so much as losing, it's already lost.

Even top players will sometimes make mistakes. Why give up and quit if you still have a 5% chance of winning or drawing through less than perfect play by your opponent or some other occurrance?
You're joking, right? You think that GMs resign in positions where they have a 5% chance of attaining a result? That's a ridiculous comment. 5%... I don't know where this estimate has come from but it is way off. Try numbers that are <1%. Ridiculous... 5%... Don't talk such crap!
That actually happens in football. I've seen games with multiple red cards where one team is playing 11 against 9, and the team with 11 runs up the score. The team with 9 players ("pieces") left doesn't then resign their hopeless position.

That actually happens in football. I've seen games with multiple red cards where one team is playing 11 against 9, and the team with 11 runs up the score. The team with 9 players ("pieces") left doesn't then resign their hopeless position.
The spectator factor has already been well discused. You've posed no comeback to it whatsoever. You can't now chose to ignore it at your convenience because you have no comeback.
5%: I should've written X%. The point is, this is scientific question. I'm going to work on a mathematic model for this. It is a mistake to assume perfect play. Here is the question to model: What percentage of resigned games would've had a different outcome had they been played to conclusion? My hypothesis is that that number (X) is greater than zero, and possibly a more significant number than most people (even chess experts) would guess. Also, in addition to looking at all games resigned, you could focus on certain subsets of games (like games resigned early in the middle game), which could likely have a higher value X than the set as a whole. So all I'm arguing is that X > 0 (which I think no one would dispute), and that it could be possible -- at mininimum -- to come up with a certain subset of expert level games where X is a more significant number than most experts realize.
Certain subsets: Say in the history of chess there have been Y number of games resigned by the player playing white within Z number of moves (pick a lower number of moves) where certain pieces are still on the board (say both queens, or some other grouping of pieces). Given those conditions, it is possible that a computer model factoring in the (very low) error rate in expert play in such situations could result in a rather significant number for X (the percentage of games that were resigned that would have had a statistically significant probability of having a different outcome had they been played to conclusion).

5%: I should've written X%. The point is, this is scientific question. I'm going to work on a mathematic model for this. It is a mistake to assume perfect play. Here is the question to model: What percentage of resigned games would've had a different outcome had they been played to conclusion? My hypothesis is that that number (X) is greater than zero, and possibly a more significant number than most people (even chess experts) would guess. Also, in addition to looking at all games resigned, you could focus on certain sets of games (like games resigned early in the middle game), which could likely have a higher value X than the set as a whole. So all I'm arguing is that X > 0 (which I think no one would dispute), and that it could be possible -- at mininimum -- to come up with a certain subset of expert level games where X is a more significant number than most experts realize.
Then take all of those same games and calculate y, z and r. y being the difference in performance level in games played shortly afterwards due to the energy drain avoided from resigning. z being the quality of life improvement from not playing out the lost position. r being the difference in chess knowledge aquired between playing out a fruitless position to no gain and spending a little more time with a clear head analysing where you went wrong earlier or otherwise just practising tactics or whatever. Then go and cry because you realise how stupid you've been to have ever thought that you had any case here at all whatsoever.

Also, just a side note. Your whole mathematical model is based upon a completely incorrect assumption. The assumption that the masters are as likely to blunder in completely won positions as they are in more equal ones. A very much won position of a similar complex nature to an equalish position would produce far fewer blunders/major mistakes from the master than the equal one because the priorities of the game have changed. Your model does not take this into account and would give horribly inaccurate results. Completely won position = fewer blunder but generally a worse quality of move simply because the mater knows all he has to do is not blunder unlike in the equal poisition where this mentality could well cost him a result.
Let me simplify things. Does anyone on here believe that if you took every expert-level game in the history of chess that was resigned and played those games out to conclusion that not a single one of those games would end in a different result? I don't think anyone would argue that.
So we all agree that the number of games that would've ended in a different result is > 0.
My question is simply what is that number? Why shouldn't we want to find out? It's possible to model that. And it's possible that that number is different than we (or even expert chess players) would expect.
Why complain? Would you literally tell your opponent to not resign one of your games?
Resignation is an admittance that you have successfully outplayed them, and it is a courtesy to the opponent to not have to sweep up the game. At my level, when I blunder a piece in a blitz game I usually resign because I'm agitated at myself for being careless. At longer time controls, I only resign if it is hopeless. Here's two example games of mine played OTB. I had black pieces in both games.
TL;DR: If your opponent resigns, shake hands and be glad you won a full point.