Not sure if i agree with most
I think tanking is a hard job, they carry the burden of the whole party. A good tank would not just tank, but find new strategies to win the fight. A good tank is never an idle tank, meaning they will always have something to do, like casting stone skin on healers, etc. The Tank job, mainly paladin, is more than just a meat shield.
When you've played with a good tank, you realize how inefficient a bad one is. The main problem why i think there isn't many tanks, is because most people stomp out learning tanks, and lump them with bad tanks.