They don't understand healing in the game (and healers thereof)
Proof of that speaking about tank remember the 2 extention in a row where paladin had by far the weakest defensive kit and no self healing because they had a GCD heal in their kit (that they never wanted to press ever)
Well healers are the same things. Somehow SE seems to think WHM is a strong healer because of Cure III which is indeed a strong GCD heal. Not understanding healers in this game want to use 0 GCD heal, and reaching that point has been a little bit easier every expansion we got