Leveling/playing DPS is actively punished

[Jaquan]

DPS will always be more popular, because it imposes less responsibility and underperforming in it is less obvious (unless you parse).

All DPS have to do is dish out damage, hopefully not stand in stupid, and occasionally do a mechanic. And there is always another DPS to blame when a DPS check fails.

Tanks have to do everything the DPS do and manage the mobs.
Healers have to do everything the DPS do and heal people.
Most often there's only one of each, and when either screws up, it's usually obvious.

As a result, there's less stress when playing a DPS, so of course more people gravitate to DPS. This is inherent in the roles, so it isn't going to change.

As compensation, however, it's been my experience that DPS classes clear solo content (e.g., FATEs, solo duties) faster.
Perhaps over time that compensates for the longer queue times, perhaps not.

Honestly this. There's also the fact that DPS simply fit the Hero Fantasy much more. They're the ones that stay in the spotlight slaying dragons and saving those in need while the rest just supports them.