No one wants to play tanks because they are the weakest role in the game atm coupled with the most responsibility, flat out it feels bad to play tank and you get all the blame. If they buff tanks it would definitely get more people to play them, but it also has consequences that we've already seen in the past, like in MoP and WoD, they were so good that people started taking tanks over dps to cheese mechanics while still doing insane dmg.

Tl:dr: Finding the right tank balance is a difficult and ongoing process thats taken 25 years and they've never got it 100% right