Except that we are
not in the entertainment business, contrary to popular misconception. We are in the advertising business, and programming the consensus favorites -- regardless of format -- is what attracts and keeps listeners. Most people expect to hear some of their favorites every time they tune in. Just because a small minority think those songs are overplayed does not change our programming for the majority. (Sorry about that, but the truth is often uncomfortable.)
Anyway, it is the number of listeners that we sell to the advertisers. With agency buys, it's format and ratings. With local businesses, it's usually the case of the owner personally liking the station's format -- again, regardless of repeat factor -- and wanting to reach others who like it, on the premise that those listeners would be good customers for the business because they listen to his or her favorite station.
And yes, in the Classic formats, there is relatively little change. Over 75% of the songs that were Powers when I relaunched The Eighties Channel™ three years ago have never moved from that category.
To the audience, this is aural comfort food. They want the "same old same old", contrary to
@AMRadioGuy's opinion.