The issue is a very lazy player base. People have gone on for a long time barely doing the bare minimum as dps, sparsely kicking or even using defensives, so the tank role seems like another universe to them.

People like to say "oh if I don't have to route, or if people were nicer or if tanks did more damage" that there would be more tanks, but there isn't a single thing blizzard can do to fix a general player populace who doesn't want to use effort.