Once in a while there will a valid reason, some sort of emergency so urgent that they don't even have time to click the resign button. But the overwhelming majority of the time it is just poor sportsmanship. You can report them: https://support.chess.com/article/675-what-is-stalling
Abandon instead of resign?


Maybe I'm doing something else that folks don't like, but I never abandon games (at least not after making a first move).
Roughly 20% of the time that I win recently, my opponent simply abandons the game instead of resigning. So I have to wait for the clock to wind down and eventually end the game. I tell myself to enjoy my victory lap, but I can help but think it seems like poor sportsmanship. Is there a good, understandable reason why folks do this?