It's more of a common courtesy thing to not pull while people are still in cutscenes, last thing anyone wants to happen is to come out of the cutscene, teleport in and immediately get killed by a wave of mechanics.

Now if everyone's just standing around and clearly not in cutscenes, and nobody has pulled yet, I'm charging in. Doesn't matter if I'm a tank, healer, or dps, I don't want to stand around doing nothing for too long.