I'm going to take a different angle on this.....I think the NCAA answers are more based on what countries these athletes come from. Tennis and soccer are international sports. In the case of tennis there was a dramatic change about 20 years when D1 coaches started recruiting the majority of their players outside the US. Their specialization started in their country because football, baseball and other sports weren't offered. The few high school age US tennis players took lessons from local pros, moved into an academy setting to get better, and play for national or regional rankings where the college coaches find them at tournaments. Hockey is a different and similiar to tennis. Talented hockey players play for private high schools and clubs and get offered or picked up in their "minor leagues" before attending college. In some cases these players have been away from home for a couple years and start college at 19 or 20.
The other part of this is that other countries don't have the athletic opportunities that US kids have, and other countries don't necessarily put as much emphasis on athletics in college as the US does. It is a cultural thing. When I was a high schooler 35+ year ago, it was all about the 3 sport athlete. Today, I think it is very different. It is more about trying to get that elusive D1/D2 athletic scholarship. The money is tighter on athletic scholarships and it is more competitive to make a college roster at any level. Coaches have choices. Do they want to pick that 3 sport athlete who did well in all 3 sports or do they want to pick the athlete who is very accomplished in one sport and dedicated himself to that sport? I'm not saying it is right or wrong, but if I was a coach that is a tough decision.
Also, I think there is a "silent majority" of student athletes who either want to use athletics as a "hook" to get into a school they normally wouldn't have access to or just because they love a particular sport. They have no plans of going professional and any athletic scholarship dollars that might come their way is incidental. it is about playing a sport they are good at, and enjoying the comaraderie of college athletics. However, they are limited to that one sport they've developed skills for due to time limitations.....they have other things in their lives that are more important.
As always, JMO.