Read about the fall of Corregidor and Singapore and the bombing of the Beirut Towers and even a REMF can predict the future.
I'm guessing the parameter of Kabul Airport is similar to Colorado Springs.
Five entry points all crowded and a limited amount of good guys on the ground because its a withdrawal operation combined with a adhoc rescue evacuation.
Impossible to screen the outside parameter.
Why didn't crowd control reinvent the bayonet? Its been a impossible operation run by yes men.