It's really not. NATO doesn't want Ukraine now that Russia is serious about opposition, but in the 2006-2009 the US was fighting really hard for Ukraine to join NATO despite opposition by France and Germany. Eventually Ukraine had a change of mind, but not before NATO formally stated Ukraine was welcome.
The move away from NATO/EU ambitions was unpopular domestically in Ukraine and led to Euromaidan, after which it turned out that NATO and co. weren't willing to back up their posture anymore.
You should listen to the talk by Mearsheimer, it's very instructive and interesting. There is a reason he is such a respected mind on geopolitics.
Oh please, US would push back against UK's .280 British small arms cartridge[0] for NATO harmonization, despite there was already ample testing shown that the more powerful 7.62mm cartridge was nigh-uncontrollable in automatic fire. Only for the Vietnam war to demonstrate the deficiencies of 7.62NATO, and then US and NATO adopted 5.56mm, proving the initial UK testing right.
If the US can make all its members adopt a small-arms cartridge despite it not being particularly ideal, the separation between the US and NATO is merely a facade.
The move away from NATO/EU ambitions was unpopular domestically in Ukraine and led to Euromaidan, after which it turned out that NATO and co. weren't willing to back up their posture anymore.
You should listen to the talk by Mearsheimer, it's very instructive and interesting. There is a reason he is such a respected mind on geopolitics.