-Lower skilled players refuse to get into tanking because of the assumed responsibility involved. Although tanking in LFR takes little more responsibility than any other role, these players are afraid of it
-Higher skilled players generally avoid tanking because they find it boring
-Bad tanks in LFR who complain about "abuse" usually encounter this because of things they do wrong, and that's an abuse that every role in LFR experiences. It doesn't make it okay, but LFR is a terrible environment do reverting, not just tanks.
-Good tanks are not generally found in LFR because they have no reason to go (they're usually geared just fine from their own guild)
-Bad tanks generally roll a tank because they feel that it will entitle them to something no matter how poorly they play, and they get upset when others don't agree with this entitlement
-Good tanks roll a tank because they enjoy the role and responsibility involved, a responsibility seldom found in LFR.
To sum it up: Good tanks roll tank for the right reasons and do well outside of LFR. Bad tanks roll tank for the wrong reasons and put themselves through hell because they're not good enough for real raiding. Instead, they complain.
These are general statements, so there will be specific examples where this differs.
The overall point I'm trying to get at is this: if you complain and point fingers at everyone but yourself just because you're a tank, you won't get very far in the game.