Putin has transformed all aspects of his nation, industrial, economic, social (religious/education), production, etc., into entirely warfare institutions. For him to try to stop that now, and to go back to a normal peacetime society, would cause major upheavals across the entire continent. Putin needs war to distract the focus of his population away from him. People are much less likely to revolt during an active war.
As soon as there is peace and his people are able to relax and to reassess what Putin has done to Russia and to their lives, Putin and his staff/cronies are afraid that there will be a backlash which could force them out of power.
Putin has put all of his chips on war and victory. It may be too late for him to 'fold' at this point in the war.