Why are there no famous black horseback riders?

I run a small ranch, and I give horseback riding lessons to kids sometimes. Yesterday, a black girl asked if she could take lessons, but I said no, because black people don't ride horses. When she asked why, I didn't know the answer, so I just lied and said that horses didn't like the smell of KFC, so she went away. But I have wondered, why aren't there more black horseback riders (and no racist answers like "the horses would be stolen by black people" please. Seriously racist people suck)