Interesting topic. I think that more HS players hurt themselves in the gym than on the field, and pitchers upper body is specific for his position, and many parents (and players) don't realize this, without the instruction of proper trainers. But I can't see any HS administration not abiding by a players wishes, so not so sure that may have been the real reason, in the end, just an earlier opportunity to be drafed.
Harper's parents made the decision to do what they did, because in reality, he probably wouldn't get pitched to anyway, it could have been a wasted year on the field for him, but IMO he will need to secure a scholarship at a 4 year school for leverage.
From what I have heard, Stock enrolled in college early, he needed some time to grow up and work at catching.