But why did US say in December 2021 and early February 2022 before the invasion that US will not send any troops to defend Ukraine? Ukraine is a non-NATO member and Biden said there is no chance of US intervention to defend Ukraine.
December 2021:
Early February 2022:
Honestly, I think this was a belated attempt on the part of the White House to inject some realism into Kyiv's negotiating position. The American decision-making apparatus is not monolithic. There are levels of imperial arrogance. Some folks are less actively malevolent than they are simply naïve and easily beguiled. In late '21 and early '22, Washington was telling Kyiv:
1. (privately) that Ukraine would not be joining NATO.
2. (publicly) that a Russian invasion was coming.
3. (again, publicly) that the US would not be riding to their rescue.
The effect of all these statements
should have been to increase Kyiv's willingness to negotiate. But by all accounts, Kyiv refused to believe that an invasion was actually imminent. And if you don't believe that, then you obviously aren't going to see a reason to revise your negotiating position. From Zelenskiy's statements, it's also clear that Kyiv continued to harbour illusions about prospective NATO involvement right up to the point of invasion.
We probably shouldn't be surprised by all this. Without speaking to the government of Kyiv specifically, we can certainly appreciate a general pattern of societies whereby decision-makers are responsive first and foremost to the domestic political pressures that impinge on them on a daily basis, and which are more clearly defined than prospect of amorphous "costs" imposed by external actors. I think we can safely assume that those domestic pressures on Zelenskiy and co. would not have been favourable to compromise.