I don't think it has run it's course. It has more to do with not having good writers or directors. The hollywood folks likely thought the lbt fans will buy anything so decided to go cheaper with hiring writers and such and not try a hard. It works for a while, but always eventually kills the series/franchise, though Hollywood never learns the lesson. If you have good writers, the right writers, and directors no reason you can't have 20 or 50 movies in any 1 movie series.