The short term purpose of radio may be to just keep you tuned in to hear the commercials, but if the entertainment supply is not fed, soon the supply becomes watered down and poor quality. Oh, that explains the recording industry...
No doubt. Radio does not help. In the case of Rock, you have the Alternative Rock format, the Active Rock format, the Mainstream Rock format. Active Rock does not like to play anything that doesn’t sound exactly like everything else on the station. Radio is important (or can be) for sales (even if they aren’t mentioning the names of the acts as often as people might like). If a rock band sounds too different from what’s currently on Active Rock Radio, record companies will think twice about signing that band, because they know that it would be difficult to get their band on the radio. So, they sign bands that sound exactly like what’s on the radio now, because they know that it will be easy to get on the radio.