The military is definitely a complex system; as are athletes. Some have recognized that D1 caliber athletes applying to the academy or any school, didn't just decide one day that they wanted to go to college; and decide to take up a sport in order to get to college. Just like the individual who spent 4-6 years in CAP or JrROTC; or the person who spent 10 years in Scouts. Or the kid who busted his/her butt for 6 years of Jr and Sr high getting the best grades they could; so has the athlete spent many years improving and excelling in that skill. I think the main problem is, the stereotype that many have, that they "Played" sports and it was "Fun". Many people don't take sports seriously. To many, it's simply something that's fun, good exercise, and a way to spend time with friends. Some don't see it as a serious endeavor with many strong attributes that contribute to the personal development of an individual. I've written a list of many of the attributes, but I'm sure most just see the words and don't appreciate them.
But this isn't just something that happens to sports and athletes. I have fun playing guitar and piano. But I bet my paycheck, that the person who studies music, practices 4-5 hours a day, is working towards being a concern pianist or a member of the professional arts, thinks that music is a lot more "Serious" and valuable than someone who does it for fun. That can be said for the difference between any person who is a "HOBBYIST" and the person who wants to do it at a higher level. e.g. professional. Sports is the same way. There's a difference between City League Soccer, High School Level Soccer, and STING Soccer. There's a difference between Intramural sports vs D1 sports vs professional.
Just because something that one person may have done for "FUN" or for "Exercise" doesn't have as serious of a future for them, doesn't mean that it isn't as serious or possibly a future profession for someone else. And therefor, developed a lot harder and with more time and commitment vs the person who did it just for fun.
And for what it's worth, the military NEEDS people to "5 and Dive". They cannot have 1000+ each year out of the academy plan to make it a career. Think of it for the enlisted folks. You have a lot of privates; a smaller number of sergeants, and even smaller number of senior non-commissioned officers, one or two junior officers, a middle officer like a major, and then a senior officer. (Talking BASIC Manning here). If all 1000+ academy grads, and the many thousands of ROTC grads who received commissions in say the class of 2016, ALL decided to stay 20 years; lets say that was about 5,000 second lieutenants. Well, 20 years down the road, you can't have 5,000 generals. Or even 5,000 colonels. The military is designed around the knowledge that the majority of individuals; officers and enlisted alike, will NOT stay for 20 years. That most will get out after their 1st or 2nd commitment.