It depends on the station and the format. Remember: I work in this business. I know who's doing what. But I can tell you that if the corporate folks thought playing unknown songs by unknown artists would make them more money, they'd do it. It doesn't cost them a penny more to add extra songs to their playlists. They don't do it because they know it will hurt the ratings.
"Unknown songs by unknown artists". Somebody had to play new artists for the first time, or else we would still be listening to Bill Haley and The Comets. Stations like WMMS, WNEW-FM in New York, KSAN San Francisco in the 70s and early to mid-80s often broke "new and unknown acts" which were later picked up by the heavily consulted stations when the acts became successful. For example, MMS was very early on Patti Smith and helped make her a star to the point where limited, timid playlist M105 (who never got anywhere near MMS in the ratings) finally started to play her. Just one track, I might add. There are very few "breaker" stations around today, and that's one of the reasons that young people abandoned broadcast radio......the stations became obsessed with just playing the established acts and the whole enterprise got stale. Maybe not to 35+ or so who don't mind endless Eagles, Pink Floyd and Billy Joel, but unless you cultivate the lower demo, you will eventually be in big trouble.
That only lasted a couple of years until the consultants came in and started narrowing the focus. By 1978, Burkhart & Abrams started advising rock stations, including WMMS. What the consultants said was right, and it all worked. That's why people like you have such great memories of that time. Everything was going great until around 1993 and that's when the music industry changed.
WMMS may have been advised by Burkhart Abrams in 1978, but they evidently chose not to listen to them! Take a look at their playlist from 1978. Does that look like a Burkhart Abrams station music list? According to John Gorman's book, they entered into consultant deals to keep them away from competition and pretty much ignored them. So long as the consultants got paid, they didn't care.
Actually, listeners at music tests pick the songs. Some big stations do only local tests, while smaller but similar markets share and/or rotate tests. But the result is that we find that tastes don't differ that much between markets and the same "big" songs tend to test identically in all of them.
Not surprising, as the regionalism evident in rock radio for many years has been pretty much wiped out by the desire to just concentrate on the big acts. If that's all the people know, that's all they will respond to,
For a couple of years until "Superstars" sprung out of North Carolina and made most stations realize that "DJ Choice" and obscure album tracks did not work as well.
It depends on how the station laid out the music. Yes, there were some FM stations who let their jocks just run totally wild, but at the same time, there were stations like the aforementioned WMMS of the 70s and early-mid 80s, KSAN, WNEW-FM and a few others who knew how to break new music sprinkled among familiar material.
And, thanks, radiofollower. Your post made me realize I had not heard "Jack and Diane" for a number of weeks at least, so I am streaming it now to considerable enjoyment.
You must not live in Cleveland, where "Jack and Diane" is played endlessly on at least a half dozen stations.