Men's soccer is like that because of market forces. The US players are competing against guys from other countries. Federal law (Title IX of the Civil Rights Act) never had anything to do with it. In Europe clubs often form their own vocational high schools (academies) and players get advanced training from early days, play against pros on youth squads, and the best are thrust into competition sometimes as high schoolers. The rest never go to college and are full time pros on minor-league clubs right off the bat.

For decades the college stop has been known as the major reason why US players never make it big in major foreign leagues, except as goalkeepers. First, it takes two to four years off their pro development while they fumble around part-time against low-level amateurs. The NCAA rules do contribute here. College years limit player growth with strict practice rules, a short season that only lasts a few months, and on-field differences, not to mention lost earnings.

The best US players now find clubs in Europe and go to their youth squads or academies. US clubs are forming their own academies too, to keep up and keep young talent from going overseas.

Same issue as the US pro sports, honestly. The NBA and NFL make rules that essentially force young players to go to college. Otherwise, most wouldn't bother. Those sports are popular only because the college game's popularity predates the pro game's.

MLB, historically, plucked or drafted most players out of high school. College was for winding down careers and getting degrees, until the 70s, when they found that baseball skills developed well in college. Today most players go that route, even though high schoolers now turn out as good. There are 299 baseball schools just in DI.