Russians aren't. Russia is fighting almost entirely with volunteers. It's illegal in Russia for conscripts to be used within Ukraine, and that law is fairly well followed. The Russians dying in huge numbers are something like 95% volunteers, and paid very well for the risk they took.

Ukraine does have the draft, and those men do get used to defend Ukraine. Also, a lot of people volunteer in liu of getting drafted. I personally know a few people who volunteered because they'd rather be able to choose their assignments.