It could be for a number of reasons but they may have withdrawn before the seeding of the next round took place.
Tournament Eliminations

That occurred to me, but why would anyone withdraw after having made it to the last 30 of a tournament that started with over 1,300 players? The only other reason I could think of was that they might have been disqualified, though how cheating could be conclusively proven is unclear to me.

I think I found the event you are talking about and the account was closed, either voluntarily or involuntarily. If that happens before all the games in a group complete, they they are marked as eliminated.

The accounts could have closed or the players could have just withdrawn. To be honest, I can't really grasp why you're struggling to come up with motivation for withdrawing. That is probably what I would do if I ever joined a large tournament on chess.com.
I would join the tournament as a way of starting some games. Depending on the tournament that could be more specific: maybe because I wanted to play people closely rated to myself, maybe I like playing as Black and White versus the same opponent, maybe because I wanted to practise a certain opening or whatever... Anyway, my point is that my motivation for joining certainly wouldn't be to win. Who cares about that? I just want to play chess. So, when the round is over, instead of waiting months to start the next, I'd just leave. Maybe join another, maybe not. It doesn't matter. I've played my games, I'm out. I don't care about progressing.

The accounts could have closed or the players could have just withdrawn. To be honest, I can't really grasp why you're struggling to come up with motivation for withdrawing. That is probably what I would do if I ever joined a large tournament on chess.com.
I would join the tournament as a way of starting some games. Depending on the tournament that could be more specific: maybe because I wanted to play people closely rated to myself, maybe I like playing as Black and White versus the same opponent, maybe because I wanted to practise a certain opening or whatever... Anyway, my point is that my motivation for joining certainly wouldn't be to win. Who cares about that? I just want to play chess. So, when the round is over, instead of waiting months to start the next, I'd just leave. Maybe join another, maybe not. It doesn't matter. I've played my games, I'm out. I don't care about progressing.
That's your opinion and I respect it, but I'm not sure it's a view that the majority of players would agree with. A sporting tournament is by definition a competetive process. I may not enter tournaments with a burning desire to win them, but having reached the last 30 of a 1,300 player event does give me a sense of achievement, and I'll certainly regard the games in the next round of this tournament as higher priority than any casual games I might be playing at the same time.

I never gave you my opinion. I gave you some facts. Some people won't be interested in winning the tournament. That isn't my opinion. It doesn't want your respect. You do what you want in your tournaments, just don't talk about other people as though they must be motivated by the same things that you are.

You stated that you would probably withdraw if you ever joined a large tournament on chess.com. You then stated that some other people "won't be interested in winning the tournament". That's your opinion. Fair enough, but my opinion - may not count for anything, but I'm entitled to it - is that that is a rather strange perspective. I can't imagine Bobby Moore saying in '66, "let's not bother with this Germany game lads, we didn't enter the tournament to win it anyway."

What the Hell is wrong with you? First of all you talk about everybody as though they share your exact views; then you made it clear that you have no idea what constitutes an opinion; now you're comparing an online chess tournament between patzers to the biggest sporting event in the world? Get some perspective.
It doesn't matter whether you think it's a strange view. It doesn't matter if you don't share it. It doesn't matter if you "respect" it. It is possible for people to have that view. That's not my opinion. That is a fact. Wrap your thick head around that.

You can speak for yourself, I can speak for myself. We can speculate that others may agree with either of our viewpoints, but that's all it is - speculation. In other words, opinion. Not fact. I am not 'thick', and if you're just going to be rude and make playground-level insults, perhaps it'd better if you hadn't bothered responding at all. Have a nice day.

Just how thick are you? I gave you the example of myself for a reason. The fact that I would do that and have done similar things before means thats its not an opinion. I do it. I am a person. Therefore it is done. Therefore it's not opinion. I can't continue this and you clearly don't want to either. Please don't reply with another stupid comment because I probably won't be able to stop myself from responding. Such a simple concept...

Opinion differs as to what constitutes fact and what constitutes opinion. That's a fact. Well, in my opinion anyway. Ok let's leave it there :-) I wish you success in your future tournaments, or not as the case may be.
I always withdraw after 1st round. The reason - I try to keep number of games at some managable level. It is possible to predict when the 1st round will start as you see it filling up. And it is exciting. But waiting for 2nd round was annoying, I just didn't want to find myself all off a sudden with 5-10 new games at some random moment .

Thanks for sharing your thoughts. I too have at times found the wait between rounds annoying, and don't like having too many games at once either. My own solution to managing 'workload' has been to play the opening moves of any new round games very slowly, to avoid a situation whereby you have many games all simultaneously at a critical stage requiring crucial calculations. Either that or resign any casual games I was involved in. Personally I'd rather forefeit them than abandon a tournament I'd made progress in, but that's just my own individual preference.

Thanks for sharing your thoughts. I too have at times found the wait between rounds annoying, and don't like having too many games at once either. My own solution to managing 'workload' has been to play the opening moves of any new round games very slowly, to avoid a situation whereby you have many games all simultaneously at a critical stage requiring crucial calculations. Either that or resign any casual games I was involved in. Personally I'd rather forefeit them than abandon a tournament I'd made progress in, but that's just my own individual preference.
WTF? You're happy to resign and discard perfectly good games for almost no reason but you can't even begin to understand why somebody might choose exit a tournament at a very logical time, for a logical reason with no adverse affect to others? All of this to the point where you start threads about it and go on to say stupid things like "that is a rather strange perspective".
On top of being really stupid and unable to grasp simple concepts you're also just screwed up in the head. Personally I don't spend hours over my correspondence games to the point where my rating is a shocking 800 points higher than tha of my blitz and 450 higher than my standard! To the point where I am moving intentionally slowly in the opening or voluntarily resigning (or claiming to) games because I don't have enough time to focus onmy more important ones... But you don't see me creating threads about such people acting all confused and retarded (well, I don't think that's an act).
Each to their own. If you want to spend crazy amounts of time on your games you do that. I really don't care. If I want to join tournaments to play chess rather than to win at all costs then I can! Don't create BS threads and tell people that they have strange perspectives when they give you legitimate answers to your retarded questions!

Chess Oath, I really think you need to calm down. You claimed that you don't want to continue this discussion, yet you then respond to a comment I made that wasn't even addressed to you with an ugly and baseless personal attack on me. Perhaps you are too ignorant to appreciate that words such as 'retard' aren't exactly socially acceptable, or the irony of having responded so many times to a thread you deem to be merely idiotic. It is possible to resolve misunderstandings or even to completely disagree with someone without resorting to abusive language, so please either keep a civil tongue in your head or keep it shut.
Rather confused after scrolling through the list of groups for a tournament I'm currently taking part in.
There were a few cases where all games had been completed, yet the player who had topped the group (and by a clear points advantage, not just on tie break) had not progessed, with qualification awarded to the 2nd placed player instead.
I've played in several tournaments on this site, and have never come across this before. Can anyone explain why this happens??