Why doesn’t the US have more pro leagues in Basketball, Football, Baseball etc behind the major leagues?

I read the other day that more than 1.000 (!) US basketball players play professional overseas - in Europe, in Australia, in Asia etc. Here in Germany for example, we have more than 100 US basketball pro players, even in the lower german leagues.

So with the US having that many good players - why aren’t there more leagues in the US? Isn’t there interest in local pro sports (below NBA/NFL/MLB level) in the US?