Miller is the fall guy. I believe he was retiring. I would bet he said something like, we need to hold onto the airbase and kabul airport. Those who know better in DC like Bidet through milli vanilli said you get 700 military to protect those bases. He probably responded it would be impossible to do so and said I can only somewhat defend one of them. So, they had their answer: Miller chose to only defend Kabul, and the rest is history.
From my personal experience with dealing with DC I learned the method they get their way is through support. Undercut the field manager by reducing resources.
I guess Miller did not hear Thatcher’s comment that she traced the decline in the British Empire by the invention of the telephone and its use between Whitehall and the field.
Miller was gone before Bagram was abandoned.