Blame all the people playing dps wanting to pewpew, and not learn how to roll a tank or healer.
Cant count how many times in TS3 or vent, that I have gotten to discussion on the amount of dps people play vs heals and tanks, and most people say something along the lines of:
"It looks too hard, I don't want to have the responsibility they have, so I play dps"
I find dps fun, tanking and healing looked boring to me, and intimidating, but I rolled a tank and a healer, and can keep up with the best, and I enjoy both probably more-so than dps.