Youth driving culture never happened before the 1950s. There was a hint of it in the flappers of the 1920s but adults controlled the spending.
Teenagers became a distinct culture in the 1950s. You can tell because adults went straight into hysteria. We look back at the decade as passive and conformist and naive but they saw gangs and beatniks and rancid music and movies destroying their world. (Not to mention that the schools we think were so great were totally failing youth, with books asking Why Can’t Johnny Read?" Don’t get me started.)
Anyway, that meant that youth had an identity for the first time, they had money and power for the first time, they were hungry to get visible and influential, and they had no competition, nothing to hold them back, an infinite world to expand into. Everything was possible. All the old rules were thrown out the window. Except that most people liked the old rules, which meant that an establishment culture existed to rebel against.
All cultures changed in the 60s. There were new waves in movies, and literature, and science fiction, and fashion, and art. Having rules to trash stimulates better art than having no rules at all. Having shockable people makes for better art than when anything goes. (IMO, of course.) Rebels with a cause make the best art, which is why the best recent art has come from groups that traditionally had been oppressed and were released: Jews, blacks, women, gays, ex-Communist countries, Asians, and now Arabs, in approximate chronological order since the 1950s.
Music of the 60s is a piece of this bigger cultural movement. Everything came together for music to burst open. Technology helped a lot. Long playing records, stereo, hi-fi equipment, cheap electric instruments, FM radio, tape recording, multi-track recording studios, all the stuff that mostly didn’t exist before WWII was now in every home and studio. Clubs could reach teens rather than only adults. Television made groups visible and accessible.
So cheap and open and ubiquitous. It would have been weird if music didn’t blossom during the 60s. And it’s not strange that stuff since has had a hard time competing. It’s all incremental because the culture hasn’t provided a similar opening for a huge burst of creativity to set the past aside. Supposedly, the Internet is allowing new forms to grow in new niches. But that’s at the point where music was pre-Elvis. All potential, with no big name to explode it. Can that happen today? I’d argue yes, but the whole point of a an explosion of new is that nobody can see what it will be until it happens.