I run into so many tanks who simply refuse to AoE threat. I wait for as long as I can on trash pulls before healing when I see only the tanks main target has any enmity on him but eventually it gets to the point where I have to heal. One Cure and any other mobs in the trash pull are on my face. I smash Fluid Aura cast repose and in the process of trying to Repose I usually take lethal damage and even if I don't the fights gone all to hell with enmity on everyone and I end up tanking half the pulls. These pulls are never marked out before hand.

I can only think of two reasons for this 1) every tank I've played with is awful or 2) they just assume everything they aren't attacking will be asleep because of Deep Sleep?