Last night I was questing on my paladin while queued to DPS a random. I rarely queue to tank as I wouldn't have any time to quest. The average wait times were between 30 and 45 minutes so I only got into 3 groups over the course of the evening, one of which didn't make it to the first boss. Why, because everyone dropped group except me.
You know how when you queue for a random as a DPS and one of the DPS doesn't accept and times out, you get another group pretty quick. This is because you are at the top of the queue. Even higher yet in the queue are groups already in an instance. Obviously this is a foreign concept to many players because no one in their right mind can possibly want to wait longer for a random. Perhaps many DPS aren’t in their right mind and 45 minutes sounds better than 5.
Another thing to keep in mind while you are waiting for the rest of your group is that you don't have to wait in the instance and do nothing, you can click the teleport out of dungeon option on your minimap and continue questing or whatever you were doing before you accepted the random dungeon. Then when the group is ready you just teleport back to the dungeon the same way.
It made even less sense last night as the group was struggling a little due to an inexperienced tank. The tank left shortly after running back after a bad pull which wasn't even their fault. Someone requeued and we'd of gotten another hopefully more competent tank if not for the healer dropping group rather than accepting a role. Both the other DPS drop right after that. Even if just one of the DPS stayed I wouldn’t of had to requeue at the bottom.
I often wish that groups were like raids in the sense that they don't automatically disband when only one player remains, just so I could stay at the top of the queue for randoms even if everyone else left to requeue at the bottom. Although you'd think those queuing as DPS would be more adept at working the system in their favor given the drastically longer queue times.