My theory is that country's performance is roughly determined by
1) GDP
2) Size
3) Sport's relative popularity
3) is key: In U.S., talented boys are likely to go into football, baseball, and so on. Talented girls are much more likely to go into soccer.
In women's soccer, some of America's most talented female athletes compete against the world's mostly middling athletes.
In men's soccer, some of the world's most talented male athletes compete against America's mostly middling athletes.
Agree this is important in raising level of women's sports in U.S. across the board.
But it can't really explain why American women dominate soccer in a way they don't most other sports.
Relative draw of soccer more important, I think.