Have you ever played, say, Mass Effect with a black character? Or Dragon Age 2? I'm not even american and i wouldn't do either, simply because i've heard enough people talk to know the voices don't fit. It's the same general concept. Voice is a part of roleplay since forever, and it can detract from the experience more easily than it enhances it if your character doesn't fit their voice. For example, in Fallout 4 i couldn't play anything other than a depressed dad going out for milk, unless i got myself the silent mod (urrah) or tuned him out constantly.
Not sure what black people you have hung out with, but they don't all talk ghetto. I know a number of people of color that on the phone, you would have no idea what race they were.
