Prior to the 60s record companies saw music in terms of classical, light/swing music, songs from the shows and spoken word. Genres like blues, folk and country got little attention.
In the 60s all these 'underground' musics burst forth and record companies ran round desperately trying to monetise them. But the artists didn't stay put. They began the 60s in a skiffle band, went rock'n'roll, went psychedelic and ended the decade as hard rockers. Or various other routes and combinations. People in motion.