People want to steamroll dungeons because so much currency (tomes etc) are needed to get the rewards. People simply don't have the time to screw around with the possibility of having their progress slowed.

In order to have challenging dungeons the grind would have to be lessened and the rewards more immediate. All paths to those rewards would need to be equally difficult.

I agree though, more challenge in this game would be nice (but with less one shot death mechanics).