Big Serge has a good writeup on it. This is now a war of annihilation. Russia tried limited war, Ukraine rejected peace and declared total war. Russia will not quit until the Ukrainian state is gone and it can no longer make war, now or in the future. To do otherwise would be to simply allow Ukraine to recover, rearm, and go back at it in half a decade or so.
. Only problem with that is Russia can't get out of their trenches and advance. They are playing the long game.
