Radio dominated the first half of the 20th century but the advent of affordable TV sets in the 1950s seemed to spell doom for the format. Yet, radio endured. Radio was able to create a distinct image for itself, separate from TV. I have own theories as to why (cars, transistor radios and the music industry) but nothing conclusive.
I’d agree with you on cars — cheap and easy to keep throwing radios in.
Sidebar: Not many classic radio shows made the transition to tv. Jack Benny, literally the most popular of shows, had a rough switch to TV because the timing was so different. For example: Instead of a foley guy doing a doorbell sound and immediately having it open, you now have a camera spending a couple seconds tracking someone walking across the room to answer a door in silence. The vaudeville structure of having a song in the middle, or trying to put on a show as the premise of the show, didn’t work (until the Muppets). Then there’s the whole laugh track or laugh box juicing issue that some railed against or over-embraced, and it all kind of fell apart. A few managed, but it was rare.