Given what time spent listening (TSL) is on your average station, most stations want to play the hits over and over. For example, you get in your car and drive 20 minutes to work, most programmers think you'd like to hear the hottest songs of that format - the hottest hits for CHR or very recognizable classic rock hits for that kind of station. So that's why they play the same tunes over and over again. I remember back in the 80's, a station in Philly, Electric 106. They played the top song every 45 minutes. I had a friend who could figure out what the next song was that they were going to play nearly every time. They did their adds for the week on Thursdays. He even figured that out!