BYU has had at least nine top-10 finishes in xc under Ed Eyestone, who started coaching in 2000. They won the national team title and were runner-ups in 2018 and 2019. Ed has coached five individual track national champions and three individual xc national champions. Sounds like they're doing pretty well.
Every runner has a small window when the body can recover fast and take on increased training loads. He is sacrificing 2 years of that window. Once he gets closer to 30 those injuries will pile up and reduce total training time. He'll be about 25 when he goes pro and only have 2-3 years of prime years left before that window closes. He'll also have a realistic shot at only one Olympic cycle (For track anyway) in Brisbane 2032. Kinda following that Connor Mantz-style path to late-age marathon success possibly at 2036 olympics.
They do it in football too, as well as other sports. I didn't want to pick on any particular athlete, but if you look for Utahans on the roster, you'll readily find guys who went on a mission, and it sure doesn't hurt football players to get two years older, bigger and stronger, before coming back to lift weights and train again. It is a key to BYU's athletic success all over the place, but also a key to their more limited professional success, given that they lose two prime training years and have to catch back up to where they were for a while before moving forward. Then they typically go pro at 24 or 25 when they should already be at their peak, so it helps BYU but hurts the athletes.