Because you're ignoring what the Russians themselves have said.
Once the Ukieburger army is gone, who is going to protect all those annexed regions? Poland? 
Like most of the Ukraine contingent on FR who don't understand anything about military strategy or military tactics, you continue to think this Special Military Operation is about "territory", no matter how many times the Russians tell you it's about killing the Ukrainian army.
It’s possible the Russians are dumb enough to think they can ‘body count’ their way to victory. America learned that doesn’t work in Vietnam, and that was with complete ownership of the skies and the firepower to win any heads up engagement.
Imagine if after Tet the US couldn’t retake half the cities the VC seized in the uprising. That’s basically the Russians in Ukraine after 2022. And now you’re convincing yourself that they’re winning a war of attrition while being driven backward by an enemy that brings online new brigades with newer gear than they started the war with.
The denial is fascinating to watch in real time.