You know, I think I've figured out the problem.

When a DPS does well, they get a high number of damage done. Positive change.
When a healer does well, they get a high number of HP healed. Positive change.
When a tank does well... the hit you take is less impressive.

Like, that's it, right there. By its very nature the thing that shows you're doing your best at specifically what your role is meant to do, either doesn't do much damage because you reduced it, or something that was meant to kill you instead only almost kills you. But even if that's impressive for a moment, in the moment of glory you're still almost dead.

It's cognitive. There is only negatives to doing well as a tank. They're just either slightly less negative, or so much less that nobody cares.