That’s not military occupations work. There are tens of millions of people in Ukraine. Even if you could kill them at a rate of 1 per second and they never fought back that would still be decades of killing. North America started with a lower population before white guys showed up and had every plague on the planet hitting the Americas at the same time to do most of the dirty work and it still took centuries. The sheer logistics of trying to kill everyone in Ukraine are just beyond the capacity of Russia to achieve, even if they didn’t resist. And that’s even assuming they lose the war, which got a lot more likely, but still isn’t a given. There just isn’t the political will in Russia to commit to centuries of genocide against serious opposition, no matter how much Putin wants it to be true.