Because if you can't take them out of the firing line when needed you do more harm than good. And working with an experienced keeper who's done it in the league day in day out is only going to help them in the longer term.
Of course there's a balance to be struck, but that's down to the coach.
Yes that is why we have the GK coach experience and older head so now we need another GK to give the experience that the coach who should have experience can’t give 3 or 4 players he has to train, so basically we hired a coach who can’t do his job.