It's also true when people talk about sending them on loan as a solution, often to the championship.
In most cases teams (particularly those in the championship) would have no interest in players who are teenagers for us.
If we are being very generous, you may say these lads could improve to be better than that level, but they probably need 30-40 games to do so. The problem is, for those sides theres very little upside taking that risk. They get all the pains of developing a player, with none of the benefit that comes.
As for Onyango, hes started a couple and then been left out of a few. That's where I expected it to be. Hes huge, which gives him a chance, but needs to learn a lot of basics. As indicated above though, the guys that level wont carry people, as they are going to be more dependent on win bonuses etc.
There seems to be this assumption that lower league football is a training school for academies, the truth couldnt be further. They're not going to have some teenager messing up their opportunity to earn money.