A few more thoughts about the "70s".
First, what most people think of as the 60s didn't really start until about 65 and ended around '74 or '75.
The "70s" was NOT all just great music - remember disco started around '75 and ruled the airwaves for way too long. Also, Bobby Sherman, Tony Orlando and Dawn, Barry Manilow, Cliff Richard abd Neal Sedaka were popular, just to name a few.
You have to look at the industry - up until the mid-60s, AM radio was the only game in town. AM was personality DJs who talked over the beginning and end of songs, non-stop promotions of the station, events and contests, lots of commercials, very TIGHT CORPORATE control over the play list and, you know, occasionally some actual music got played.
In the mid-60s this new thing came along FM. Since no one knew what to do with it, they let the hippies take over and made it free-form - very little promo activity, no contests or events, the DJ played whatever he/she wanted to play (the more obscure the better) and they never, ever, EVER talked over the beginning or ends of the songs.(A Pet peeve of mine). Of course, these stations became popular but they never made any money so the corporations started stepping in.
By about 1975, the Album Oriented Rock (AOR) station became a popular model - you played hits off the LP instead of off the 45s and there was still some flexibility for the DJs, but the promos started creeping in along with contests and events and giveaways.
Finally in the early 80s the morning zoo arrived and radio was almost completely ruined. The final nail in the coffin being national syndication of Howard Stern in the mid-80s (Here in Philadelphia the final nail also included the great local college station becoming a corporate controlled Adult Album Alternative format).
My conclusion is that "the 70s" allowed for a great flourishing of many types of music in large part because Corporate wasn't paying attention. To the extent that nothing really new or innovative gets air time anymore, it's tight corporate control of the playlist.