A C17 is very vulnerable on take off and landing. The entire country is owned by the Taliban, and there are also rogue former government forces.
So far, the Taliban have been keeping a tight reign on their "core" forces - no attacks on foreigners, no going wild on the civilians, they are being very disciplined and the Taliban leadership is communicating.
But there is no one Taliban. There are a bunch of warlords. The Taliban have clearly put the most level-headed, least kill all infidels commanders and troops in Kabul. who the fuck knows who is in charge - if anyone - out in the boonies.
So you land a C17 on an improvised landing strip. Load it up. Send it up, and it gets MANPAD'ed or just Soviet AA'ed.
Now what, smart guy?
In a very real sense they should have tanks and MRAPS and thunderrun everyone out to China, but that's got its own level of hell. You could try another *Stan, but they are not going to want to piss off the new political force and they are not going to want Afghans in their borders.
There are other geopolitical calculations to consider (principally about people putting their feet on your territory and you now having responsibility for them even if they aren't your citizens) but I don't feel like getting into them.