What do you guys think is the cause of severe lack of Tank users?

[SamRF]

I wonder what it would be like if Square Enix released potions without recasts so that tanks and dps could heal themselves quickly up to full without a healer. And we all know the sheer outrage from developers and players alike at the thought of tanks doing dps that threatens the 'real' damage dealers.

So by that same token, why do we have game design that allows non-tanks to pull mobs without getting instantly smashed into mush? Why do we have bosses that tank themselves? Nobody wants to play a role that lacks impact. Why is this such a difficult concept?

Sometimes feels like tanks are only necessary to catch tankbusters. Other than that they're just there to increase efficiency in most content it seems. I agree this shouldn't be the case.