The problem is most Russians are not feeling much pain. High energy prices have allowed Putin to mostly insulate the economy from the effects of sanctions and a strangle hold on the media has been effective at keeping Russian public opinion mostly on side. Putin still has the option to go to a full war footing and general mobilization. If that happens he can bring a lot more manpower to the war.
This option would obviously be time limited before Putin risked widespread popular discontent, but it is the obvious next step if you agree Putin is in a must win at any cost scenario.
Putin is betting he can outlast the Western resolve to back Ukraine’s resolve to defeat Putin on Ukrainian soil. The one thing he can’t afford is another major loss of the territory he has already won.