What gives with the current crop of 80's/90's indie heros reforming?

Gang of four
Pixies
Dinosaur Jr
Slint

I'm sure there are others too that I can't remember right now. Why has it become de rigeur to regroup and play a few shows? As generally there seems to be precious little new music coming out of these reunions, is it all just about tha benjamins?

I really regret not seeing Dinosaur Jr back in the day, but not sure I want to see them now.... it's not the same.