The state department is always like that. They want to remain until the very end, perhaps as a sign of support for the government, but who knows. If you pulled them out earlier, it would be viewed as a sign of non-support for the government we installed. We always think the evacuation will take place in a nice, orderly, efficient manner.
I was working for JUSMAGTHAI in April of 1975 when Operation Eagle Pull, the evacuation of Phnom Penh was done. It went like clock work. but we pulled everyone out 2 weeks ahead of time before the fall of Phnom Penh.
Still in Thailand when Operation Frequent Wind, the evacuation of Saigon was done. It was a screwed up mess. They waited until the last minute to even start it, it was chaos from start to finish. Evacuating folks on the last day, the last hour. The North Vietnamese could have stopped it in its tracks if they wanted to and took all the Embassy folks and other contract civilians captive. But the North Vietnamese let the evacuation continue basically unhindered. That was one heck of a mess. A total screw up. Only the mercy of the North Vietnamese stopped us from losing thousands of Americans. I think the North Vietnamese let the evacuation continue mainly because they didn't want American civilian captives. The NVA had captured Ton Son Nhut Airfield, so helicopter from the embassy was the only option left thank to piss poor prior planning or should I say waiting too long.
Now Afghanistan, we'll never learn. Operation Eagle Pull, the evacuation of Phnom Penh proved it could be done properly with little fuss and very efficiently. If we do it before the last minuet or even the last second.