And KYW isn't a great reference with a full-power FM simulcast.So why isn’t one of the AM stations in Philly doing oldies? Except for KYW...
Why would they want to? The audience for AM itself is shrinking, no person under 40 wants to hear music (or practically anything at this point) on AM radio that is old enough that it is obscure by modern standards. Not to mention that they don't have to pay royalties or licensing for the music. A satellite-fed talk format is way easier to operate.
50's/60's oldies is a moribund format and is not gaining traction anywhere.

