There are basketball courts available everywhere, and all it takes is ONE basketball among ten players. The requirements for baseball are more complicated and expensive.
There are other reasons, too. Baseball skills are often imparted by a father. Even within basketball, the skills developed vary by socioeconomics. A good jump shot is not developed on a public court, where a player must struggle to get his hands on the ball. A jump shot is developed through thousands of shots taken at a basket at a suburban home.
Or it could all just be racism.
I disagree with some of your statements. Many black players certainly take a lot of solitary practice to work on their dribbling, shooting, and moves. And you can be sure if any black player shows early promise, practice time and coaching on technique are provided by an assortment of people.
+1 to your comment about the complexity and expense requirements for baseball being a major factor.
Consider that the requirements for hockey are higher than baseball. What are the racial demographics for that sport, again?