For comparison, Ukraine's military is quickly replacing its old Soviet junk with more modern (sometimes top of the line!), advanced western weaponry while Russia is replenishing its equipment with... even older Soviet junk. Even if Putin is willing to throw more bodies into the meat grinder, the average lifespan of a Russian grunt will diminish at an increasing rate. Russian bodies are piling up faster and faster as WW2 equipment is no match for modern warfare.