I think it's the actual design of the 2 tank classes and mechanics of certain fights as well contributing to the tank issue. I am betting a lot of tanks will quit tanking in the 40/50 level range.

Issues I saw with tanking:

targeting system sucks no matter what way you alter it

global cool down/animations are to long

switching targets every ability is just tons of fun

interrupts and stuns on the gcd?! I'd like to meet the designer who had that brilliant idea...

aoe threat is laughable especially at the lower levels coupled with the fact you have no aoe taunt

boss mechanics that you have to run and get adds, move from an aoe, and re-position boss every 5 seconds guarantee your going to have threat issues because you cannot get more than 2 hits in between movement

anyhow just my opinion and I am definitely retired from tanking