It's probably God.
In all seriousness, I just don't think there's a very large demand for nets in America, so people just don't steal them. I've definitely played and practiced with my fair share of posts without nets, in the 90's almost every net was years old and had holes in it. I can answer some questions in terms of my city, because I know my old coach has paid/used funding to get our goals, he probably has six around the city. In fact, one practice we spent the entire time fitting new nets onto our goals, he loved new shit. I'm just happy that we have goals in so many different parks, nets or not.