Doesn’t the title say he was promoted into the first team? Or has he been relegated again?
A bit of semantics really. While he is technically in the first team, and will regularly train with them, he’s still a part of the reserve set up as far as I know.
Generally young players have a bridge period. They’ll be “promoted” to the first team, but instead of just training with the first team but not actively involved in game plans / not getting so much as a sniff of minutes, they’ll spend times training with the first team and be gradually blooded but also still be a part of the reserve set up. You’d pretty much stall development if you took all actual game time off the hands of someone who isn’t actually ready for proper first team duties yet, but is still ready to be involved in the set up.
I think a good general plan is excel in youth set-ups, having a bridge season to blood them and maybe get some minutes here and there and to understand the first team procedures, roles, reality and then spend a season or two on loan somewhere. Loans are a good chance for a regular step up to the adult game, bigger stage and also moving away and developing as a person.
Obviously not one size fits all, you get some like Greenwood who immediately go to the first team, some others might be ready for a loan before a bridge season, or whatever permutation.