Why should a song only be around 3 minutes?

Personally, I feel if a song is really happening, 4 to 4 1/2 minutes is OK.  Anything longer, you start to lose the listener. So why 3 minutes? Most writers I know are looking to get their songs on the radio. I have heard many reasons for the 3 minute rule. For me the most believable reason is advertisement. The more ads a station can sell, the more revenue. First of all if the songs are too long the listener is going to lose interest and change channels. When that happens enough, the station will lose its ad-buck rating and the price they can charge for ads will go down. Fewer songs = more ads which = more revenue for the stations. Contrary to popular myth, radio is driven by profit, not music. Have a question? We would love to answer it.