OP: Just in case it isn't obvious from the other posts in this thread, the reason for the long queue is the 2000% chance for legendaries to drop. Anytime that buff is activated, the PTR fills up. A good chunk of this population are people just screwing around and eating up resources while not actively testing anything.
It's kind of shitty, but it's completely expected considering that the entire point of D3 is to collect legendaries. The PTR community buff is basically cheat mode for these players, so they're out having a blast while it lasts.