How many of those poeple played tank just because of fast queue times and being able to do damage on par with a DPS? You can say they have been made simpler, but I would say the previous expansions were more detrimental to a tanks gameplay than we have now.

Tanks are now tanks. They take less damage than everyone else and deal less damage than DPS. Enmity is purely on the tanks rather than being at the mercy of whether the DPS decided to pop Diversion/Lucid Dreaming. That was just unnecessary busy work and I would frequently on my Monk generate enough enmity to rip the enemy away from the tank, even using diversion, just because the buff window just didn'y line up with Diversion. You can say, well, use enmity combos/switch to tank stance, but then you are just gimping yourself not because of your play, but because of someone else. People also say homoginisation is a bad thing, however i would argue that some form of homogeneity is needed to prevent some tanks from being taken over others.

The main issue with tanks right now is not tank design, it is encouner design. With bosses auto positioning themselves, no real reason to mitigate tank busters in non extreme/savage content etc. Improve the encounter design to accomodate tanks better and people might start coming back. Tanks were 'simplified' for a reason, however, that reason hasn't amounted to much.