Come on guys, in Europe cycling has always been a sport accessible to all. Most of the greats came from working class backgrounds and most young aspiring pros today live on very meagre incomes. Go to Belgium and see the amount of kids that are squeezed into team houses just hoping to get a shot at the big time.
Today you can pick up new bikes good enough to begin racing on for under 1000 euros, a lot less if it's second hand - not a major obstacle for a working class family of any colour if that is the sport their son or daughter wishes to pursue.
The economic argument stands up for sure in large parts of Africa and Asia (where distance runing is clearly amongst the cheapest sports to participate in), but across Europe and the US where there are tens of millions of blacks it doesn't stand up.
The vast majority of white and black kids that are athletically gifted will opt for football, tennis, golf, rugby, American football, baseball and basketball because their friends play these sports, their dads and big brothers play these sports, their families go and watch these sports.
As the kids grow up other things become obvious. These sports all potentially pay a lot more for the average pro than cycling, they are perceived as more glamorous and less demanding of time. Compare the average salaries of pros in these sports to a cyclist and you will see the massive gulf that any parent can see to.
Maybe the society and community that we grow up in has the biggest influence over what sport we choose. We play what those around us play at.