Are you only doing the bare minimum as a healer, just healing? Most people will give the healer comms if they are stance dancing and have very good dps while keeping everyone alive. I main DRK, if the healer does this, they get the comm. Else the comm goes to the dps that did the best. If the healer and dps were bad, I just leave without giving a comm. Plus if you are doing this and aren't giving comms, remember comms aren't a guarantee, players give them to anyone for varying reasons.