Probably the same reason why a working class white kid in a Northern mining town can't either.
Look at the British equestrian team, names like "William Fox-Pitt", cleary a toff twat and I'm sure it's the same with other countries.
Black people might and probably do have a genetic advantage when it comes to sprinting but when it comes to something that involves skill it's less to do with biological genetics and more to do with the fact that the opportunities aren't there for the vast majority of the population to participate in competetively.