Why do radio stations have such limited playlists?

Radio stations I suppose only tend to gravitate towards popular demand, the selections are always thought out to appeal to most tastes. for example I am nearly sick of ACDC becasue they are played multiple times daily on the classic rock stations, but ACDC has many fans.

I interned for a radio station and here's what I heard. They put the most request/popular songs in their play list or rotation. At the station I was in it was all computerized. The DJ just sees the next song, announces it and presses a button. If a request comes it then can add it in if they want. But they pretty much have a group of songs which they play in high rotation then added other random songs the DJ picks. The more popular or requested the song it, the more its played. Thats pretty much how I know it goes.

Oooooh,,i think once you as a radio DJ you will know why lol,,

Many radio Stations are limited space, they have music that is called in, emailed,or how ever they seem to what to learn what people want to listen to. Requests, After a month or so, they then start cutting off songs that have not been requested, and the new ones begin. Its a cycle. This is why it is very important, if you want to keep hearing your song or songs you keep sending requests to keep them moving. Also, depending on the station, whether they play them or not. You have so many different stations with all types of music. Today the country music there are songs that use to be considered rock and roll. and the class of music has been renamed.