That's true, but hitchhiking declined in the late 70's, well before podcasts, Spotify, satellite radio, or even books on tape, so the availability of alternate content can't have been a factor.
Instead, I've heard a variety of alternative reasons for the decline in hitchhiking:
- govt and media fearmongering about dangerous hitchhikers - increased police enforcement - higher rates of car ownership - the Interstate Highway System made pulling over safely more difficult