I've actually had the exact same situation happen to me as my SCH on dungeons.

I don't mind not getting commendations, but I notice i seem to be less likely to receive them the worse the party is. I see a DPS pulling horrible numbers, another DPS pulling mobs from ahead, a tank that doesn't use CD's or only does single target threat generation.. despite all of this, I receive no commendation.

I've actually received waaaay more commendations on my SMN than either my PLD or SCH since expansion hit.