A lot of their HITs are phone calling. If someone snags the HIT and the needs to wait until they have quiet time or the office they're calling is open then yeah, a lot are going to expire. I know I've accepted some of theirs to audit the phone calls (not make the calls), but if it says in the HIT that the call is 10 minutes long and I realize that I've got it in my queue when there's only 5 minutes left on the timer (because I often forget to check timers in my queue), then yeah, that'll expire too.