a country can only be so good at so many sports of this type. Every american playing basketball, or baseball, or american football, or ice hockey, is one not playing football. You have to understand that for many countries, the dream path, the default one, for a very athletic young person who is interested in team sports is soccer, from the age of 6 or younger. The entire structure above that branches outward based on this huge intake of talented children, with vast institutions of professional coaches, academies, and huge amounts of training and game time with other talented people, no matter where in the country they live.

Learning to play well heavily depends on exposure to an appropriate level of play that challenges and stretches young athletes. If they get to a level thats too challenging, they aren't picked for match day, don't play, and wash out. If they stay at a level that isn't challenging enough, they learn bad habits that won't work against much stronger players. Thus, even those few americans that do play a lot at home struggle to make the jump to play against teams from outside, because the level of competition overseas is so much stronger. This is why for many many years, everyone on the mens football team played and lived in europe (and usually grew up there in these academies, too). The only way to develop players at home is if you can convince enough of these highly skilled players and coaches to move to the US long enough to play against the developing players, so they can hone their craft in a way that actually works against the best in the business.

This also explains why the women's game doesnt see the same problem, becuase that massive infrastructure in europe and the rest of the americas doesnt (or rather, didnt) exist to the same degree for young girls.