What killed Rock Music?

Its been going on in my mind lately. Rock music was at its height of greatness in the 60s and 70s with great bands like Zeppelin, Pink Floyd, The Who, The Beatles, The Doors and many more. Then in the 80s Queen was the big rock band and ruled the airwaves. I'm not sure what happened in the 90s but something made music take a new direction. Then it became the muck we have now. What I want to know is WHAT HAPPENED TO GOOD OL ROCKNROLL.