Soccer is cheap compared to football, baseball, and ice hockey. The same holds true for the NBA in terms of highly-paid coaches, camps, training, etc. The US only has one pro soccer league.
I think another poster had it right that many other countries just don't have sports leagues like the US: NASCAR, NBA, NFL, but they do have soccer, so they focus on that sport.
There is no doubt that there is greater competition for the sports dollar in the US. It is the world's largest sports market. That said, countries like the UK and Australia have competing sports like cricket, rugby, and Australian rules football. Basketball is a major sport in Europe now. I have attended two European final fours in basketball, one in Spain and one in Israel. The fan followings are tremendous. Basketball is the number two sport in Greece.
I think the NFL, NBA, baseball, and Ice Hockey would not want to see soccer rise to be a major sport in the US. The timing of the season would have an effect as well. LA is a hotbed of soccer drawing about 25,000 a game in MSL play. The growing Hispanic population will aid in soccer's popularity.
Club soccer is very expensive with the traveling and tournaments, especially in big states. My parents spent around $5,000 or more a year for me to play soccer. Basketball cost us around $250. Baseball was around $500.