As an American who's never left the country, I feel like we just have too many sports to focus on Soccer. We divide our athletes up into too many categories and don't really leave a whole lot of room for smaller, more up-and-coming sports like Soccer. Aside from the fact too that we've been playing other sports for a lot longer than we've been playing Soccer. American Football, Basketball, Baseball, Ice Hockey, Golf, Tennis - too many sports, too little fans.
And also, we like sports with scoring. Ever wonder why the NFL is sooooo huge here? It's because pretty much every time a team has possession of the ball, there more than likely going to score. Soccer sometimes goes for entire games with no teams scoring, so we just lose interest.
But I really like soccer, used to play it for a couple seasons when I was younger biggrin