Are you basing this on the cast times you see next to the healers names?

Using heals with cast-times is pretty much the last step in the process of keeping you alive for me, since the instant/castless ones are generally free. On both WHM and AST it's not unusual to wait for the tank to get low, since benediction (WHM) will totally refill your HP in an instant and now has a much lower CD time, so it sees more use than before but is most practical when your HP is lower, and Essential Dignity (AST) is more potent if you have less HP.

If your HP isn't getting low enough because you're using Clemency, you'll see less heals incoming.