Short version: Bob Dylan witnessed the powers that be segregate the musical landscape after rock and roll pioneers were bringing races together through music. The powers that be made sure that things couldn't get out of hand.
The full article is linked at the end of this excerpt:
A Journal of Musical ThingsBob Dylan Explains What Killed Rock'n'Roll-And It's Not What You Think - A Journal of Musical Things
Interesting. Not sure who did what. But certainly there is a racial divide. Black rockers and white hip hop artists are rare. I even see it with kids who feel that hip hop is for blacks and country is for whites.
Now was it to keep people divide or marketing strategy who knows.