Originally Posted by
Seraphor
To be fair, this is done (in general) in dungeons.
So I think this is at least partly due to how easy the instances are. When someone is in a cutscene in a dungeon, you wait, because you either can't do it without the tank or healer, or being down one DPS will make it take longer anyway so you might as well wait. (or, at least some of the time, just basic human decency)
Castrum/Prae are so easy you can complete it with half the party, or even just a good DPS and a good healer.