Is there a reason why this ability can't crit for mages, yet it can for the other classes? (Can't confirm for clerics since I don't play mine much)

In all my time since I've gotten this ability, I have never once seen it crit when used on myself, and it's righteously annoying to watch a rouge or warrior use this while I'm trying to kill them in PvP after they've CC'd me and it crits and heals them for 70% of their health. Whereas any time I use this in PvP I'm lucky if it heals for more than 3k a tick.

Am I crazy?