It's far too difficult to find a decent tank. If you don't have a tank most dungeons are going to be miserable or even impossible.
Not only is it so hard to find a tank, but in most cases they can't even hold threat.
I feel like I'm punished when I want to play my GS instead of my BM because I end up having to tank on GS... Not fun. I like gearing up but the more gear I get on my dps classes the more often I have to tank on them...
From my experience as a BM main( that recently has been playing more GS) I can say from experience tanking just isn't fun or rewarding on almost every boss.
Bosses (AND TRASH MOBS) CC melee far too much where ranged rarely have to do anything.
Would being really good at fighting every boss and mob in the game mean you have no issue dodging every attack, knock back, knock up, knock down, stun, daze, grab, and pin? Yes.
Are the majority of BMs and KFMs you find in f8 going to be very good? No, no they're not.
Make tanking more enjoyable so more people want to do it.
Give the one with aggro cc immune
Give tanks more threat
Give them more dps
Extra rewards
Hell, add a new super awesome high damage TANK class to the game ( I'd personally reroll to a class with a greatsword and happily tank everything if it was available)