Folks who blitz move in longer time controls, why?

I've noticed this quite frequently when I play 15/10, that some opponents don't even use their full increment much less the original time on the clock. Why play longer time controls if you do this? The guy I just played blundered a mate in 1 and had 16:46 on his clock, almost 2 minutes more than he started with, meaning he used about 90 seconds for the entire game. I don't get this... why not just play blitz or bullet?

I wouldn't worry too much. Just take the dub and free points and go next.

People just play at the pace that suits them no matter what time control the game is. Each to their own. If it costs your opponent a loss to you then you should be happy. Winning is difficult enough so take the easy ones when you can get them.

Many players are accustomed to playing faster time controls and bring that habit into longer games. They may not consciously adjust their pace and continue to play quickly out of habit.