1) A player's level is not dictated by the performance of her team.
In the case of the U15's, say all 5 YNT players are on the field. That is just less than half the team. I know one is midfield and one is a forward for sure. Say they have another 2 def. and another mid. BUT say the 2 at defence are wingbacks, or even better say that one is a wingback and one is a center back. That leaves one wingside with a NON YNT player. It may leave a whole left side or right side without a YNT player. Say the play a 4-3-3. I know for a fact their GK isn't a YNT player. So that is 3 on defense who are not YNT memeber and 2 who are. Are those two supposed to fill in and make up for the NonYNTness of the other players, including the GK?? In midfield, say, if it is a 4-3-3, I know that one player is a center mid, probably playing attacking, so you have two other mids, one of which is also on a YNT. What if, and this could be the result of a look over or a risky choice that will increase chemistry between some players or something, but what if the one other mid is on the same side of the wingback, and what if that wingback plays with the other YNT defender on her side? That leaves, so far, the entire left or right side open except for the CAM.
Sorry for the whole mini stimulation, but my point is that one player, or two, or five, cannot carry a whole team. A team is a team for a reason. That does not mean that the player isn't good or should be a YNTer. It just means that she is a teammate.
Also, for a lot of these girls, I believe it is their first full year, or second, together and are having major chemistry issues.