This is a great point. Music use to be everywhere from tvs to movies to drug stores, elevators, etc. Everyone heard many of the top 40 so a common language and understanding existed.
I don't think there is a mainstream anymore. The only place to hear popular music is advertising and it is always from much earlier eras.
Shows like WKRP cannot work anymore. You can't even get it on dvd because of the music licease demands.
Todays popular music are highly profitable but only heard by a small group.