Okay, you got me there.
It's a two-pronged problem, and more oriented to radio than TV (though not completely). People (not demos, actual breathing adults) over 55 stop hearing programming they enjoy because the companies that advertise through agencies stop buying stations that are heavy in those demos. So you don't hear "your" music because the companies that support the stations that used to (or might in the future) play it won't buy you if you do. Getting that message across to listeners
might motivate them to stay away from those advertisers until they indicate to stations that they will return to supporting them if the stations add back that era of music again. Not return to a 100% older music format, but not boycott that era or style in their mix either. I write this with R&R oldies in mind, but it could just as easily apply to other forms of programming (e.g., classic C&W, smooth jazz, standards, whatever). "I support P&G when I buy Tide, but P&G won't support KRTH if they dare play music tailored to 55+ that grew up on that music. So I don't buy P&G products until P&G makes it clear to KRTH that if they re-introduce the occasional Beatles, Stones, Motown, etc. song in the music mix, we keep buying the station." Is it going to happen in the real world? About as likely as finding ham on rye served at next year's Passover seder, I guess.
To your point, you're going to hear ads anyway. Why can't some of them return to being creative enough to influence me to retry their product? I can afford Tide as well as the hypothetical 30 y/o housewife, but at the moment I have no reason to spend the extra bucks to select that option over the better deal I see at Costco. Maybe hearing some of "my" music in close proximity to "your" spots might make that association.