Pretty much as Rein says.
Our gameplay experience devolves as we level up. Leveling dungeons can be fun and exciting to heal, with some being notorious for forcing us to be awake and on the ball. Expert dungeons? Absolute snooze fest. Slap a regen on the tank, asylum/soil on the ground and you might as well AFK for the rest of the pull for all it's worth. And don't get me started on bosses. 24 man? Arguably even worse.
Not to mention that the skill ceiling now boils down to remembering a cooldown spreadsheet and simply not healing as much as possible.
Not healing = healers in a good spot? Really?