I was talking the history of early rock bands with a 13 year old who asked why the first bands were all British. I explained that rhythm & blues music was essential to the development of the genre. most R&B bands were “colored” and at the time no white station and no white venue would allow them to play. So a lot of them tourred Britian, which was more accepting of their music.
When she recovered fom her shock, she asked me the OP question. And I did not have a clue what to answer her.
I’m talking ROCK here, not rock and roll.