it's a risk acceptance thing. The AF has decided which is the appropriate level to accept certain risks, and to what authority it can be delegated. It's not just "because", it's because at some point, someone at MAJCOM staff ran a risk matrix and decided what made sense for what level assumes/accepts a given risk. I can definitely say you won't have much headway on lowering that acceptance level, but you may have better luck requesting an update to the MEL (using your example).