The NFL, the NBA, and the NHL are all predicated upon size. The bigger you are, the stronger you are, the more successful you can become.
Soccer isn't built that way, you can be 5'7", 150 lbs, and be successful.
Here;s the problem though. You can be successful at that size in baseball, too, and we all know where the roots of the country are in regards to sports culture.
The ONE sport, like soccer, where size doesn't really matter, also happens to be in the same country where the one sport that has been a tradition for almost 150 years shares that same idealogy