The interest of western powers was never really to save Ukraine, but to use it as a tool with which to grind the Russian army to a pulp till it no longer is a threat and can be brought to be complacent to western demands (providing cheap gas and rare earths again), similar to how the western powers used the Soviets to grind down the Wehrmacht even if they didn't actually like or cared for the Soviets at all.
Ukrainian youth and oligarchs with money moving west to raise birth rates and property prices is just the icing on the cake for the western economies.
A depopulated Ukraine is also good for them. More places to mine for rare earth without NIMBYs getting in the way.