Oh I was just thinking about it, and one huge reason we probably don't have a show until the 25th is Lorne hates when a NFL playoff (or any other live event, I guess) bleeds over into the show's timeslot. I remember the show actually got higher ratings with the audience spillover, but Lorne is a stickler about the show starting on time.
I'm not sure if they know or can even accurately guess the dates of the playoffs on which channels when they set the schedule for the show over the summer, so it's probably easier just to wait until they are over. (And even if they go long on another network, it would prevent people from switching over.)
But yeah, Lorne HATES the NFL messing with his show.