In the city, little kids learn to swim only if their parents take them to the pool. And they learn to swim well only if they go a lot. The Unified Field Theory of black-white differences in 21st century America probably comes into play here: it's harder for single parents to make the time for this, especially if the local pool isn't within easy walking distance and you don't have a car.
In my old neighborhood I remember as a kid hearing constantly about black kids drowning in local lakes and canal’s when they would be playing on rope swings off trees that would eventually have the person wind up going into the said lake or canal. Why even take the risk if you know you can’t swim at all?