Obvious after Afghanistan that the current administration and the military it controls isn't capable of the executing the logistics involved with evacuating non-embassy civilians. If the US can do it right, who can? I would say they're erring on the side of caution because they don't won't the another PR hit. Embassy only they should be able to protect and evacuate, so it's not the same concern.
Set aside a Russian invasion, which may just be US media bluster, and consider a scenario where foreign corruption peddling is revealed in the Ukraine, and the Ukrainians decide to take revenge on anything foreign. Hostages, would be lucrative, for example. It might be that the war drum banging is just a pretext to hide a cut and run caused by some other event that the administration doesn't want to make public.
I hold the thought, as well, that Brandon knows there will not be a Russian invasion, but he's talking shit and threatening to be able to say it was his policy that kept the Russians out of the Ukraine. Saw last week that some MSM outfit was praising Brandon for "masterfully" getting NATO on bard. A true statesmen, Brandon is. None better.
If I'm Ukraine, I've got to consider that if NATO moves in, then NATO can start shit with Russia. and the Ukrainians are SOL. Let NATO in know, for example, and your prospects for peace are in the hands of some demented fuck in DC who give two shits about Ukrainians caught in the crossfire. If I'm Ukraine, I've got to consider that re-aligning with Russia might be the best move going forward. I think Zelensky mentioned such an option, as well.