“The Dictator’s Handbook” is a great book that argues (convincingly) that countries “act” not in their “own” self-interest but in the self-interest of their leader.
Which is always to stay in power (and maximize their power).
So I agree as short-sighted and bad it would be for Russia to do this, if it helps Putin stay in power right now, it makes sense.
Emperor has no clothes scenario. Everyone is telling him his army is strong and can steam roll Ukraine. Meanwhile his army consists of untrained men in rain boots whose leadership has no idea how to fight but is really good at stealing everything not nailed down.
If there was a greater interest at play Russia would be a very different place, and Ukraine would willingly join their sphere of influence.