Playa in September?

We have boiled down our hotel choices to the Alhamba with an ocean view balconey or Playa palms. We noticed that the prices drop off in september though. We could save $120 on a very nice room at playa palms by delaying our trip two weeks to the first weekend of September. Question is why do the rates drop off so quick in september? Is it huricane season? To hot? or just everyone goes back to school and work?