How is FFA different from Solo?

Everyone seems to think FFA is different from Solo since in Solo everyone loses points if they don't get 1st place. It seems to me that practically there is very little difference in terms of the strategies that you use.  In the beginning stages you work with your opposite and try at least not to lose first and get 4th place. Once it is down to 3 players there is no difference between 2nd and 3rd in both FFA and Solo if you are rated over 2000 (you get a +1 or -1 in FFA) So in both games at this stage the only goal is to go for 1st without regard to the risk of ending up 3rd!

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Well one of the major reasons you work with your opposite in ffa is so you don't get last. In solo you don't have that motivation so you "team" less with your opposite.

Why would you team less. The first step to winning in Solo is also not to be last!

Once you get to 3 player game it's up for grabs usually

From my experience with FFA and Solo (keep in mind that I am <2000 in both, bullet doesn't count), because in FFA getting 2nd also awards points, people tend to be more lenient as they know that in the case that they don't get 1st, they can still play for 2nd (which is one of the reasons why hyperbullet FFA is super annoying). Because of this, players are willing to coordinate with their opposite (usually in 2400+ games, anywhere lower and it's basically a 1v1v1v1) in the hope that they don't get last, like @Chestnut924 stated. In solo, it's a different story. Giving a player points in exchange for piece activity doesn't work as well because the player who has the most points wins, not the most pieces. However, you will still see teaming in these games. Here is an example (bullet, yes I know, but it's a good example): https://www.chess.com/4-player-chess?g=9534332

In this game, I got teamed on by blue and green (and yellow too, though unintentionally) and somehow survived for almost 15 moves before getting checkmated. As you can see, teaming in solo is still quite common, but it doesn't benefit the players much. Green got the mate in this game and proceeded to win, while blue didn't get anything as placing second is a loss too.

I don't understand. Doesn't the one with most points win in Solo? Or is it last man standing?

No matter how many pieces remain or whoever the last player remaining is, the player with the most points wins.

If it is most points then I don't see why you can't sacrifice points for activity in both Solo and FFA

btw I am about 2200 in FFA and have only played a little Solo

(I am 2000+ in rapid + blitz solo and 2600+ in rapid ffa) I think that there is a significant difference  between solo and ffa because in the three player stage of ffa (assuming everyone has more points that last place), there is no risk of losing a significant amount of points (e.g. -20) because 2nd and 3rd increase and decrease your rating respectively only slightly. On the other hand, in solo, in the three-player stage, 2nd and 3rd will lose the same as 4th.

Again, I'm not even that good at solo or FFA, so I don't know much, but I would think that giving a player 20 points for a queen doesn't help much in solo. I've played quite a few FFA games in which I've gotten a checkmate but losing my queen in the process and still happened to win the game. I've also lost games where I got a queen in exchange for my opposite getting mate.

Maybe players play illogically for 2nd in FFA? Even though they get 1 point maybe it feels good to many to be in 2nd?

...especially in hyperbullet...people target other players trying to "bring down their time" while in reality they're just wasting time trying to attack someone. Then either they flag or get mated because, in both cases, they aren't paying any attention to what's going on

Sometimes, in the three-player stage in ffa, people get upset with others' play and kamikaze on one person in order to achieve 2nd place and prevent the other from getting 1st. This happens quite a bit. 

It's ok if you've not that good. This is logic and at the 3 player stage over 2000 in both games only first counts. So logically there should be no difference at that stage. Maybe at the opening stage people aren't as afraid of 4th as much since it isn't a disaster in Solo like FFA? I still fail to see how that will affect play in most cases because in both versions you don't WANT 4th but maybe you play more defensively in FFA since it is so horrible points wise to be 4th

Can't someone kamikaze in Solo too if they are unbalanced?

In high-level solo, people would not kamikaze because it would result in losing a significant amount of points, equivalent to the amount of points lost by last place. 

Anyways even if you are right gg, this is not a major difference between the versions of rules

Most games there is no kamikaze and I would argue that in very high level games the players are more likely to look at things more practically and just go for 1st in Solo and FFA. You don't get to very high ratings by getting emotional at the board!

I don't see any practical difference at the 4 or 3 player stage if people play logically and also realize 3rd and 2nd are the same result basically in FFA