i think some healers quit to play anything else. The good point is, other healers are easily taken in groups, no matter the spec.The damage are too spiky, too often. Sometimes it's a nightmare. The timers are ok, but the healer's job too hard.
Healing some 20s on my 434 Mistweaver, have to regen each 2-3 packs and use personnal defensives cds on dangerous boss abilites coz they oneshot me if I don't pop them.That's difficult, but at the same time it's better than sleeping in dps.