NATO doesn’t want to become an actual war party if they can help it, and instead want to contain the conflict within Ukraine, hoping that will be sufficient. So they try to do what they can within that constraint, and within each member country’s domestic political constraints, as of course its citizens aren’t eager to get drawn into a war, or to otherwise suffer from their country’s involvement. At this point it’s also unclear what China will do should Russia start losing the war due to more direct NATO involvement; and finally there’s the nuclear risk.

On the other hand, if you let Russia roam freely and restrict yourself to formal protest, that would set a very bad precedent, and would only encourage further military operations by Russia and other authoritarian parties wanting to expand their sphere of influence. Last but not least, Ukraine is a significant agricultural and mineral/metal producer in the world, which the West certainly doesn’t want to see under Russian control, not to speak of Ukraine’s role in the geostrategic importance of the Black Sea.

Slowly boiling the frog worked pretty well during the Cold War. There's no reason to think that it can't work again. If we keep the pressure on through proxy wars, diplomacy, and sanctions then the Russian empire may eventually disintegrate further.