Hence the annihilation

The Russians know even if they win all they will get is a hostile population and the possibilities of decades of insurgency

So from their point of view it maybe better if the ukrainians leave Ukraine or are annihilated

It's one of many reasons why modern war is so destructive it's not enough to conqueration

You've also got to conquer the people

To put it in context let's say a nation conquered America

What do you think would happen and how would the American people behave