Pragmatism
If Russia takes back Ukraine all they’ve done is go back to 1992. Meanwhile, they dump their entire military arsenal down their shirt front destroying city after city and wiping out their youth generation (in the midst of a demography crisis). It is worthwhile for the West to take advantage of the opportunity to modernize its military and hand over its obsolete inventory to Ukraine to help out their endeavour.
Interestingly, China proposes to do the same thing to itself over Taiwan, with the identical demographic crisis).