.....ohh
Why do people keep resigning?

it's a great question which I used to wonder myself. however, as you gain elo/rating, you realize that it's going to be harder and harder for your opponent to blunder, as they are experienced. especially if the odds aren't in your favor -- you have less time, less pieces, less rating, etc --. I resign now, but not very often. In my opinion, I think you should keep playing if you believe you might have a chance to win (if it's a hard endgame where you are losing but it's hard to convert, a middlegame where you are down the exchange but there are complex tactics, etc). That's my theory.
I've noticed that people resign when they could have kept up the fight, too.
... but I'm also guilty of ragequitting as well <_<