Increasing xp gained by dps classes in leveling dungeons

[Arrius]

More precisely: Every game with enforced roles suffers the same problem.
Even League of Legends had it with the Support role that nobody wanted to play. That increased queue times the moment they implemented a way to queue directly for a role, to the point they had to create an auto-fill option where people get forced into the role to solve it.

Because those are roles with responsibility to others than yourself, hence its avoided by the majority of the playerbase - They got enough of dealing with that in the Real World, so why bother with it even in the game?