FIFA has rules for players when deciding which national club they may play for. This includes allowing young players, such as those in the United States men's development academy, the opportunity to play for a nation's youth teams (Under 17, Under 20, etc.) and still be free to change teams if they have a legitimate claim to representing that team. However, once a player makes an appearance in a FIFA sanctioned international match (such as the FIFA World Cup, CONCACAF Gold Cup, a qualifying match or sanctioned friendly match) for a national team, that played is cap-tied to the nation.
Most coaches will not call up academy players directly to the men's national team, as they are still developing teenagers who would be playing against far more technical and strong grown men. However, the US Men's National Team (USMNT) has recently called up young players with no professional experience in an effort to cap-tie them early and because of extreme talent. Jordan Morris, a forward, was promoted to the USMNT while he was still a collegiate soccer player at Stanford University in 2014. In 2017, forward Josh Sargent, just recently graduated from the US Development Academy in St. Louis, was called up to the USMNT.
As the USMNT looks to do better developing young talent, more players like Morris and Sargent will get opportunities to play for the USMNT and become cap-tied to the United States. While we have not seen a player directly called up from an academy, the youth trend could certainly change that.
The United States Men's National Team (USMNT) has yet to win the FIFA World Cup or establish a reputation as an elite team, the United States Women's National Team (USWNT) is the top team, winning the inaugural FIFA Women's World Cup in 1991 and two more in 1999 and 2015, while never finishing lower than third place. Why is this? Most simplistically, it boils down to Title IX and women's athletic development outside the United States.
Title IX, in the most simple definition, is a law put into effect in 1977 mandating equal access and resources be provided to both men and women in education. The impact of this law is most obvious in collegiate athletics; a college cannot spend more on men's sports than women's sports. With the economic dominance of football, a male collegiate sport, and men's college basketball, on most college campuses, athletic departments had to dramatically increase spending on women's sports. The long term result was women's sports, specifically in basketball and soccer, dramatically increased the quality of the players.
For the USWNT, a pool of extremely talented and technically skilled players where graduating from college every year. Even with no consistent professional women's soccer league, the USWNT was able to field a starting IX and full roster of talented players by virtue of the college system.
Compared to other nations, the development of men's soccer players in the United States has only recently become comparable. For years, academies of even the lower division clubs across Europe and South America dwarfed the limited resources being funneled into the sport. This led to a quality gap that still exists to this day.
However, no other nation had a similar collegiate system as the United States. For the USWNT, as other nations continued to spend millions on men's national teams, the US was the only country consistently developing female talent. When FIFA officially created the Women's World Cup, the USWNT dominance led other nations to begin spending on development for women the same way they did for their men.
Today, the USWNT are still the dominant team in women's professional soccer, but the gap between them and the field has shrunk dramatically since 1991.