Granted that the markets for various teams don’t necessarily follow political borders here, but really, I think that it makes sense that they don’t. With national teams, you have one team for all of Brazil, and then one team for Luxembourg. One’s drawing talent from a much larger pool than the other. Here, on the other hand, teams are wherever there’s enough population to support them: There’s no Wyoming team, because there just aren’t enough people in Wyoming, but there are multiple teams in each sport in California, Texas, or New York, because those places do have enough population to support multiple teams. The end result is that our teams might not represent specific states, but they do all represent roughly the same number of people (except for the Packers, but that’s just because the people of Green Bay are insane about football).
Now, one thing that might be different between US teams and international teams (I don’t know whether this is the case in international sports) is that players are relatively liquid: Teams trade players all the time, so a fellow who used to play for New York might end up playing for San Francisco a year later. Does this happen at all with, say, the World Cup?