I actually find the focus on hard DPS checks pretty interesting though.

The thing about tanking and healing alone is that traditionally they are pretty binary, you either pass or you fail (either you die or you don't) and getting better and more geared at it just means you spend more time twiddling your thumbs. DPS on the other hand has no ceiling and more is generally always better.

Tanking and healing are really boring to me when they don't have that kind of continuous progression that DPS has - it's very satisfying seeing a boss die faster and faster as you get more geared. They would have to design some mechanics for tanks and healers that bring that same sense of linear progression.