There are a combination of things to why there are so few white American players in the NBA, and this is strictly my opinion. First, a large majority of blacks grow up in urban areas and have little financial support. This breaks down into two categories. One its way more expensive to play a sport like baseball, hockey, even football to a certain extent, compared to basketball where you just need sneakers and a ball. All the other sports require a lot more items to buy in order to play. The second reason is that if you have little money you're outside doing other activities instead of sitting at home in the house watching tv, on the computer, or playing video games.
The second reason why their are so few white players in the NBA is because of the way Stern decieded to market the NBA. They highlight the one on one, superstar player, instead of the team player. They banned all zone defenses to help achieve the one on one game. We all know a player like Wally Szczerbiak (yes I know he was born in Spain but just follow my point) can't guard a superior athlete like a Dwayne Wade or Paul Pierce. Stick Wally in a zone defense and hey that would help a ton. I know its a stereotype that white people are slow and black people are more athletic, but it is true for the most part. Yes defense is about effort, but athletically I'm willing to bet 9 out of every 10 black males are superior athletes compared to white males. So not only would that help them on defense, but also players like Redick and Wally would be much more useful and spotting up against a zone defense.
Again I realize its another stereotype that whites are better shooters, and this isn't really an argument because when you get to the NBA you should be able to shoot from distance, but its one you could make. Its more so a case for the defense of white players than the offense, but it goes both ways.
Those are really the main arguments. The money one is the better of the two arguments but that's just my thoughts. I don't really care much for NBA basketball outside of the Celtics because its a one on one league instead of a team game like high school and college is. In the end I don't care if you're black, white, yellow, green, purple, whatever, if you can play ball and you put the time and dedication into it odds are you'll get far.