U-21 teams

I couldn't get to Blues last night so watched Cheltenham comfortably beat West Ham U-21's.

Whilst development squads are obviously important, it did get me wondering why they continue to U-21 level. If a young player isn't breaking through into the senior squad at 19/20/21 are they simply at the wrong level?

I saw nothing in West Ham's team that would get anywhere near the level they need to be.