Rock and Roll came about at a time when there was a great deal of social change going on and this infused the music but the music also infused the protest and social action. So one could say that rock and roll was kept alive and vibrant because of the hippie movement.
Hippies were very open minded, free people who supported expression through music. Even if they didn't prefer hard rock or metal, that openness and acceptance definitely contributed to the popularity of Rock and Roll. Once people realized that other genres of music are out there and pleasurable to listen to, it would be much easier for different genres and bands to gain exposure and popularity.
Of course hippies are the reason rock and roll exploded and maintained popularity. People with conservative attitudes at the time were appalled by these artists, but none the less they had talent and they received recognition for it. Hippies provided the ground work for a lot of the ideals we see in today's society.
While it may seem like hippies were the main catalyst to making rock and roll famous, the answer is more than likely marketing. The hippies would have never heard of a lot of the bands had it not been for major labels marketing them out, so while the labels were corrupt, they did spread music.
Hippies are not the reason that Rock and Roll exploded and maintained popularity in the US and the world. Rock and Roll music is simply just really good music that was enjoyed and shared by a large portion of the population. I think the hippies helped, but they were not the reason.