You would think that once the song was ok'ed to be used in that show, it could be used forever.
No. The music was licensed for broadcast television... its CBS play, and aftermarket TV syndication.
30+ years ago, no one had the foresight to contract licenses for home video. If Fox wants to put an episode of WKRP on DVD, and it includes music by Foreigner, Billy Joel, Aerosmith, Donna Summer, the Stones, etc., then the owners of that music are due
additional royalties.
As a result, WKRP on DVD is cost prohibitive. Season 1 went forward, but with extensive music replacement; as a result of the replacements, sales tanked.
If you and a few thousand more consumers are willing to pay approx. $100/season with the original music, let 20th Century Fox know, and maybe they will consider your proposal.