The Soviet Union lost 20m+ dead because they faced an existential threat from an enemy that intentionally massacred many millions of people who lived there (including people who weren't particularly enamoured with the idea of a Soviet Union or Stalin as leader)

The situation isn't quite that bad in either Russia or Ukraine which was also one of the constituent parts of the Soviet Union. But it's certainly closer in Ukraine, even if most Russians hold an irrational level of enthusiasm for the war