For 99% of good high school runners, the only tangible benefit financial or otherwise, is help with going to college, either a scholarship or just a boost getting into the school of their choice.
For the true elite, good enough to consider being a professional runner, they should be training at "college level" at 17 or else they are going to be way behind their peers. To assume at 16 that they are so super talented they are going to be able fall way behind and make it all up later is a really bad gamble. That is not maximizing your potential.
So a great high school coach is working their runners hard to maximize their potential benefit, and for the vast majority, that will end up being college placement and getting close to their maximum running potential as a senior in high school.
Also, we know from Soles himself (and from his past runners), that only a small subset of his runners on Great Oak did the elite training. Everyone else is training at a level similar to any of a hundred other good high school programs. These runners are generally not scholarship level runners, so elite training doesn't make sense.
If you are one in a 100 million runner who wants to train elite level in your teens, but without the burden of a high school racing schedule, then don't be on a high school team, get a private coach.