Black v. White Music

I was shocked to learn that MTV refused to play music by black musicians, even with Michael Jackson's popularity. Playing Michael Jackson would only have helped the network so why is it that this amount of blatant racism was occurring and acceptable? Today there are genres that are predominately one race, like hip hop for African American musicians but there is more cross over and popular music relies heavily on rap. Was it that even as far into the 80s there was still the divide between "black music" and "white music"? "White music" being the mainstream?