https://www.thedrive.com/the-war-zone/42128/what-the-u-s-militarys-options-look-like-for-extending-evacuations-from-afghanistan
Afghan billions
This piece spells out some of the options before us in the withdrawal, and a key point I had missed is that the US has frozen billions of dollars of funds, pending completion of the withdrawal. This is key, and explains why the Taliban are being cooperative.
Article also points out how vulnerable the planes and the tarmac at Kabul airport are to mortar fire. They are in easy range and basically sitting ducks if the Taliban decided to do something.