I already tank, but most often its that there is too much pressure or expectation for tanks.
In raids, tank messes up usually means a fast wipe. Making the mistake very obvious.
In dungeons, tanks are expected to know their routes and generally how to lead.
Go to slow people tell them go faster, go too fast group often dies.
Every other new class had had a tank spec…problem is still there. Why would another spec suddenly magically fix the problem.