IMO, professional soccer in the US is way behind because it’s less TV friendly. No commercial breaks (other than halftime) means less money coming into the sport than more commercialized competition.

At youth levels, it’s one of the most played sports in the country. Then as soccer-playing American kids get further in their “career”, they get pushed toward other sports where more money is. Colleges rake in cash on football and basketball, and lots of these kids play multiple sports until a coach makes them choose.