Biden and NATO have ruled out a no-fly zone over Ukraine, saying that enforcing it would put the U.S. and NATO in direct confrontation with Russia and would expand the conflict.

With Stinger missles and the like, Ukraine is managing to survive.
NATO's sanctions will be biting with full force in another two weeks, so there's no need to give an ever more desperate Putin an excuse to unleash weapons of mass destruction and risk WWIII.
Putin blundered! We're seeing signs of him looking for a dignified exit. Lavrov has mumbled something about a negotiated settlement in the form of a neutral Ukraine. In the form of Sweden, that would probably be acceptable.