Does anyone know why Simpsons reruns are like the same 15 or 20 episodes?

I don't know how it is in the rest of the country, but here in Chicago
our Fox affiliate shows it 3 times a day (5,6 and 1030), and they
rerun the same episodes over and over. I wouldn't mind as much if
they were decent episodes but they're suck ass episodes from the last
few years. Anybody in the television industry have any insight?