It was all up to the corrupt CIA. Without a doubt they promised millions, maybe billions, of dollars and I believe, and God help us if I am right, the promise was to leave behind some Americans (for propoganda purposes). There is no other explanation. Seriously.
I believe you are right. The kind of deal our State Dept. would agree to. Sadly.
I have long suspected the Americans are not allowed to depart so that a great victory can be declared on their release after a successful negotiating session with our new Afghan partners that have come into the light of modernity.