I have wanted McAtee to make it at City since forever but I guess he is just not showing it in training otherwise I think that he would have got more time.
Certain youngsters like Eric Garcia and Rico Lewis seem to have earned Pep's trust and so get to play whereas others don't even if, to us, they look like more accomplished footballers. I think Pep values what he perceives as "football intelligence" which he seems in very few players. Gundo, the Silva's, KdB, Rodri, Stones and Fernandinho (somewhat to Pep's initial surprise) have this and so get deployed in varying roles. Other players like Grealish, Mahrez and even Foden may not have this to the same extent and so get to play more limited roles.
Not sure whether can be learnt but McAtee and the other youngsters need to be up for whatever is asked of them to make progress and earn Pep's trust.