Such as Thordan...

It could allow us to know before queing if someone is new or not.
It's really boring to have people joining when you ask for no bonus and are pretending to know the fight but actually don't.
It makes everyone waste time for nothing.
You'd say, we could just kick the bonus, but it's not easy to figure out who it is,and we don't want to endlessly make new pf (because of course, people will or give a chance to the bonus or just leave).

At least, with raid finder, we knew before if someone didn't meet the condition to enter the duty.