I'll repeat:
When a station gains the perception of "repeating songs too often" the reason for those complaints (other than pure mechanics) is excessive play of mediocre songs.
So when a listener tunes in, instead of hearing "favorites", they hear so-so songs... songs that don't have strong passion and strong positive feelings.
And if a listener hears that kind of song often, they feel that the songs are repeating. It's not any actual individual songs that are repeating... its just songs the listener does not particularly like that create an impression.
The fix for this is to cut the lower scoring songs out of the library. If the rest of the station is well executed, the ratings will go up.
However, over time we have seen stations that don't understand... just as you don't... that "repeats the songs" does not mean that the library is too small. So they increase the song count in the name of variety, and are a) mystified and b) fired when the ratings go down.
David, David, David...
Even as you acknowledge, songs can fall into and out of favor. But you don't say WHY a song that was once good is now "mediocre". In many cases, it is because it was overplayed ad nauseum. "Brown Eyed Girl" and "My Girl" are and were great songs on their own merits - the songs did not get worse, stations like KRTH played them into the ground and ruined them such that I and many others never need to hear them again. So it is not just hearing mediocre songs repeated that drives listeners away. In fact I can't even think of a "bad" song that has made me forsake KRTH and other similar stations - It is the overplaying the "good ones" everyone is complaining about.
Same thing on the AOR side. The two Boston albums that came out in the 70s are great albums, with some amazing muscianship and in some cases, good songwriting. In the 70's, I couldn't get enough - that is until corporate AOR radio came along with their testing and shrunken playlists to make sure I not only got enough, I got it rammed down my throat for going on 30 years now. Nobody takes the band seriously (well their 80's material helped in this department, but I digress) even though they made a couple of the best album rock records of all time. What I am trying to say is, where once I liked, now I flip - automatically. Again,it is not the songs themselves; they never changed. It is radio and radio alone that ruined them.
Lastly, the idea that with a limited playlist people can go weeks and months without hearing a repeat based on "similar listening patterns" is simply a statistician's fantasy. *People don't live like that* and I bet many people hear the repeated songs (you know, the "good ones") many times in one week, even though they "play at different times". I know I have heard multiple repeats in a given week on KRTH many times, and for that station, I am definitely a "casual listener" at best.