Kinda similar to England and football. Some if not most of the best footballers came from the cockney areas of east London or south London, the coal mines of Newcastle, the factories and mills of Leeds, Sheffield, the rough docks of Liverpool, Manchester, Portsmouth, Southampton.
Similarly, America's best athletes have come from poor and working class areas. Before the modern era when baseball was the number one sport, the best players came from the rural south and midwest (Ty Cobb, Georgia, Hank Aaron, Alabama, Mickey Mantle, Oklahoma) or inner city kids, especially immigrant kids (Lou Gehrig, German, NYC, Babe Ruth, German, Baltimore).
Poor kids don't have as much access to soccer leagues. Soccer leagues are either in Latino neighborhoods or the suburbs. Inner city blacks play basketball mostly, football as well. There are very few youth soccer leagues for us.
Maybe in time. I think if blacks had access to soccer at a younger age, we'd have a top 5 team. I'm hard pressed to think of one sport that blacks in America adopted and we didn't dominate it to a large extent internationally (basketball, athletics, boxing). This works as well for black women (basketball, athletics and now more are having access to gymnastics).