(On my phone so no edit....)
Added to the above:
I think theres a shortage because (a) people like to kill stuff, faster the better; its cool (b) people like to heal, pull off epic times of keeping everyone alive and noticeably DPS (c) it takes tons of patience to stand there, dodge, and not be the major factor involved with moving the battle forward to a kill, but waiting on the rest to do it, and be the one to blame if you didnt dodge all 6 AoEs while keeping the mobs in place for melee, or use your CD soon enough so healer could DPS too, thus died causing a wipe, (d) it does get critisized and knocked more than DPS or healer (I have a WHM i76). I think it is mainly A and C above, then D and then B in order of why theres a shortage.