What about the idea of the American Dream, and the potential huge rewards per sport?
If we can make the assumption that afro-americans are overrepresented in 'below average income households' in society, would it make sense that they pick certain sports over others, because they yield higher rewards, if one accedes to the pro league?
American football, and basketball seem to be the equivalent of soccer/football in Europe and Latin America. At least a great number of Latin Americans try to escape poverty by becoming a great soccer player. When one succeeds, multibillion dollar contracts have your name written on it. And especially in the case of soccer and basketball, the initial investments are low, you need a ball and a hoop/goal and that's it. In all cases, soccer, Bball and Football, have a huge bling factor.
Cycling doesn't have the same exposure, and perhaps that's the reason, rewards are a lot lower. On top of that, it is considered a, and often even overly romanticized, 'hard sport'. Everyone recognizes the ugly, mudheads in P-R, teeth gritting faces when the lesser climbers attack a steep gradient, dramatic falls and broken bones... I doubt the term 'Flandrien' would resonate well in Afro-American, heck, even Latino, or White communities. In today's society, where fast money is the rule, from Wall Street to Sports, to revolving door Government/Public Service, why would anyone become a cyclist?
Isn't it like telling your parents that you want to become a miner instead of a lawyer? They would send you to an asylum!