Personality shortcoming.
Abandoned games

Too many possibilities:
Entitlement
Immaturity
Irresponsibility
Rudeness
Spitefulness
-OR-
Technical difficulties
Spontaneous combustion
Arrested by the chess blunder secret police
So while it is frustrating, just remember that the worst possible explanation is not necessarily always true. Regardless, this is why I don't play lives games longer than 10 minute rapid.
Whenever someone does appear to have abandoned the game, I'll send a quick chat message reminding them that "stalling/quitting games" is a reportable offence on chess.com. Depending on what happens after that I will either block, or block and report them or not.
Why do people abandon a game instead of resigning? Is it some sort of punishment by making the opponent wait for several minutes. What's the purpose? This makes no sense to me. I think it's just plain rude.