I'll try answering that:
One reason is the same reason that white people said that I listened to "n*gg*r shit" until hip hop turned primarily gangster, because they like to image themselves as gangster, or it gives them some kind of vicarious thrill.
Another reason is that for some reason, unlike other art forms, people generally only give music a few seconds to "hit" before they lose interest even if they otherwise spend their time with highfalutin' intellectual shit which would be the equivalent of "art school bollocks" in other forms of art.
Some people try to justify such things by saying that "low" and "high" art are the only worthwhile arts, because you def don't wanna be "basic".