Unlike most other servers, you don't get the option to look at a plot chart and select opponents by rating and game length.
So, if your say, 1200 getting paired with someone 1600, it makes little sense to keep playing. There is a very tiny chance a person 300 or more points lower couid win the game, but's unlikely, so most players would rather resign and hope the get a new opponent with a rating closer to their own.
Generally, a much lower level player has a greater chance of pulling an upset the longer the time control. With bullet chess, it's unlikely. And the ratings loss for resigning in the lopsided match is miniscule for the lower level player.
EDIT: Basically to keep order, and in line with every other chess server, games with 2 or less moves are considered abandoned. In Chess.com, too many abandoned games will lead to sanctions and even the much dreaded "poor sports" flag. That's why people will play at least 3 moves. Some will play a few more, but most players can figure out inside of 10 moves if they have zero chance of winning against a much stronger opponent.
Look to the my games. 3 moves, 7 moves, 10 moves. And they surrender. What is that? Bots, cheaters or what? I cant normally play with they. And they in EVERY GAME. How that is possible?