Why didn't this argument apply to hockey, volleyball, soccer, softball, baseball, etc. where year-round clubs have taken over??
You could just do all training for those sports through the school, right? But families don't do that (anymore).
The basis of my argument is really no more complex than: just because, for some reason that to me is not apparent and has not been explained by anyone here (I don't know if it is really explainable), it hasn't happen so far in football, is not proof that it cannot happen in football.