With a goldmine of classic hits out there (thousands of hit singles from the late 1960's through the 80's that are just in the top 20), it's really a wonder and a Sherlock Holmes mystery as to why only 400 or so are ever chosen at any given time, and it's usually the same titles (the cores, with a few extras thrown in). It's been this way for decades. The only thing that may shuffle the lists are demographic shifts over the years. I rest my case.
As Eduardo pointed out, either in this thread or another one, it's the stations that pick which songs they'll test. So how do we mere listeners know that they tin-eared suits running any vintage format radio station only submit the same handful of songs for testing?
How can any test audience possibly listen to the thousands of songs out there? One of the local classic rock stations I listened to in Pittsburgh once, as a stunt, played their entire music library in alphabetical order. This "A to Z" stunt lasted well over a week, with no song repeated. We're talking around ten days of continuous classic rock songs played 24/7. If the songs' average length was four minutes, that's around 3,600 songs.
So how does a radio station test thousands of songs to find the ones that work? Based on what goes on the air based on those tests, it appears that not many songs even get tested. Then the suits hide behind the fiction "we only play what tests well". There's no way on God's green earth that any radio station can have adequately and accurately tested over 3,000 songs to find the puny little 300 song playlists that they insist are all that we want to hear.
They claim that stations do better with tight playlists, but anyone with any common sense must realize that there are many, many factors that go into how successful a radio station is at attracting and keeping listeners. Broadcasting doesn't take place in a vacuum. It's not just what any given station plays, it's what their competition is playing against them. It's how well promoted they are, and how effectively they reach out to people who don't listen to them to persuade them to switch over and give the station a try.
I'll guarantee that any business, regardless of what it is or does, that makes a change that will attract new customers
who know about the change runs the risk of losing older customers who don't like the change. Any business. All businesses. This isn't something exclusive to radio. So, if a radio station makes a change, any change, but doesn't follow up with an effective promotional effort to inform there non-customers of the new change will usually find that they lose old customers but do not replace them with new customers. But, any business that improves their operations
and lets non-customers know about those new changes, is likely to add more new customers than it loses.
You do not have to be an industry insider to notice the lack of effective promotion for radio stations in media where non-listeners might see the promotions.
There are large groups of people who are very happy and satisfied with the programming. There is a small handful who want something else. For them, there are lots of other devices.
But that "large group" keeps on getting smaller and smaller.