Fighting Russia or the US is basically the same; you're just going to get nuked. Ukraine doesn't get nuked because Russia isn't in a real risk of losing it's own territory and doesn't want to annex irradiated lands.

But also Europe (besides Ukraine) doesn't have much to gain from fighting Russia. They're happy to assist in air raids in North Africa / Middle East for energy reasons (see Libya) but it's fighting for practical purposes.

The table can also be turned against the US. Despite the endless complaints about Mexico sending drugs & drug dealers into the US it's not like we are doing effective (or drastic).