The west has to balance providing adequate arms and not getting bombed/invaded themselves. They only do invasions on enemies they think can't defend themselves.

They thought the sanctions would do to Russia what it did to Libya, Venezuela, Iraq, and many others, and that they'd only need to drag this one out to win it on the economic rather than the military front. That obviously hasn't worked, so rather than broker the peace talks a majority of Ukrainians want, they're escalating because they don't know how to do diplomacy, they only know how to do extortion. They're talking about "negotiating from strength" ffs.