Speaking only for myself.

I stopped raiding for one very simple reason: the attitude of the majority of raiders I've come across has been absolutely atrocious. I play the game to have fun, not treat it as a second career. Maybe I just have bad luck (which I'm sure most of the raiders will say, since no one actively wants to admit they're that bad), maybe the raiding community is just that pathetic, I don't know but I'm certainly not willing to spend more time finding out.