Originally Posted by
polyphonica
Because when you are in a partial party, your party's withdrawal causes the entire queue to recalculate. That one person's cancellation was a cancellation for your entire group by proxy. The benefit of partying in a group is that you get to play with friends and often have faster queues, but the drawback is that one person's cancellation causes the whole group to cancel, and repeated failures can result in this 30-minute wait. Yes, if those players were not grouped, they could individually "troll" the same amount of times on their own, but the system has more flexibility for re-juggling that responsible person in the queue (i.e. push them down the priority list) and prioritize the ready players. Because you're grouped, though, that person's failure means that many less players are available since they can't split your party.
In other words, the system considers your party a single queue entity, and has to juggle your group around as a whole. Hence the punishments have to be applied to the queue entity as a whole in order to reduce the likelihood of successive queue failures.