Most of you are missing the point of the original poster. It was: "there doesn't seem to be a lot for the over 40 crowd to listen to".
And there won't be, either. Though, more specifically, it's the over 50 crowd that's really feeling this. And, there's a reason. The older you get, the less attractive to advertisers you are.
That's why the "old" WGRR went away. Their audience got "too old" (mostly over 50). Once that happens, advertising goes on the decline. Advertisers use means other than radio to reach that older audience.
And don't bother making the argument about how the Baby Boomers are living longer, and keeping a more active lifestyle, and have more money. It's all "blah blah blah" to the advertisers, whose eyes glaze over as you make that sales presentation, only to reply to you, "So...when are you guys going to get with the program and play some 80's and 90's music?"
All of these library based music formats will eventually die, when their listeners hit near that age 50 mark.
As for wishing for the "good old days in the 60's and 70's when rock stations had big playlists". What killed that? Stations who came on the air with more focused (shorter) playlists. Almost universally, those stations cleaned the clocks of those big list "prog rockers". History shows this to be true. And the few stations that survived, adapted.
Corporate radio has little or nothing to do with it. Advertisers are king. And they, much more than the people in a corporate office, are responsible for a good portion of why radio does what it does today. Now, add what stations are learning about the audience from the PPM (in markets where they have it) and you'll discover that the audience really doesn't want "the good old days" to come back. They want stations lean, trim...they want what they want when they want it...and...they don't want it with a lot of "jock interruption".