Earlier quoted context omitted.
In the NBA, it IS genetics. You cannot increase your height through your own efforts, the limit IS genetic. Basketball is one of the few sports where genetic advantages are a major factor. The reason many black americans are so tall is some part a cruel history but an equal part genetics - you would be foolish to deny this. The location of basketball courts is incidental and i'm not certain what your point is.
There are about 130 thousand people 6' 6" or taller in the US: https://static1.squarespace.com/static/585718168419c246cf6f2... Which is coincidentally the average height of NBA players (meaning almost half of them are below this height). There are a maximum of about 600 NBA players at any given time, so a little more than 300 at 6' 6" or above. Having good height genetics means you have a 0.25% chance of being an NBA…
However - and this is a major issue - the outliers aren't captured in averages. I read a book called Taboo by John Entine that went into this exact issue. The issue is that the outliers are what determine champions at the elite level and people with west african heritage have slightly more genetic advantages - notably in sports like basketball. there is also the issue of rising incomes and the breaking down of societal barriers. As more black americans have access to sports like basketball, more of their slight genetic advantages can express themselves. All this gets masked by averages.
Entine's book makes a point in passing - africans will slowly start to dominate sports like football (soccer) that were traditionally dominated by white people. The french men's and women's football teams are showing this, as are many other european football teams. Football is more about skill and places less of a premium on height but there is one role where height is important - the goalkeeper. In the french squad, all their goalies except Lloris are either black or mixed heritage.