i don't think that's true. soccer is one of the most popular sports in the us to play, and tons of people watch mexican and euro soccer. americans like to watch the best, and the american league is minor but growing.
I know a few US based footy fans - I'm a Glasgow Rangers supporter myself, and luckily we've won the league title this year to stop our great rivals from winning 10 titles in a row - it was poetic justice after what happened to our great club in the past!