To me, it boils down to LOVE. When someone is so engaged; enmeshed; addicted to; obsessed by; in love with what they do, they get good at it. When that love spills over to others who share those feelings, they band together and, with luck, create greatness. Then, with luck, the greatness finds itself in the hands of others who share the love of the craft to the degree they have become adept at getting it out to the world. Once out in the world, with luck, it catches on.
Rock has injuries: its ego was badly bruised by the young-uns picking up the EDM, Rap, and video game torches, but rock is a temporarily semi-dormant, seething dragon, waiting for the perfect moment to emerge from its secret hiding place, anxious to devour all doubters.