More engaging gameplay suggests more damage buttons, and I don't think healers want more buttons just to deal the exact same damage. Like if healers had 2-3 DoTs but the exact same potency, all it adds is a higher chance of messing up and dealing less damage without the reward, and then you have fewer GCDs to heal when you need to. There are also so many oGCD heals now that it shouldn't matter that much anyway.
