I don't know what country you're from but if you don't think there are subcultures in your country under-represented by the dominant media I'd assert you're almost definitely wrong. Perhaps it feels a little strange from the outside that such a subculture is definitively "black" but yeah, that's basically how things are in the US. The country has a deep history of racism and black people being literal slaves, in that context it isn't surprising that a distinct culture developed.
But I don't think the divide is anywhere near as insane as you're imagining. People don't just belong to one culture and ignore any external infulence. Black, white, Hispanic, Asian, etc. people all watch the NBA, NFL, watch Marvel superhero movies, so on and so forth. It's just that everyone also has additional niches.