It has nothing to do with intelligence. You, like many others, are posting this from a Western point of view. Russia sees Ukraine as existential. They have been saying this for decades. It doesn't matter if you or I agree, what is important is what Russia thinks. Putin will never retreat from Ukraine. He cannot politically and will not because he sees a Western oriented NATO driven Ukraine as the beginning of the end of Russia.

He said almost exactly that in his speech at the start of the war. Either Russia will be destroyed by this war (and maybe all of us with them), or there will be a new world order.

I think Putin could have found a way without committing a war crime to make his point clear, but what is clear is that we in the West have ignored Russia's red lines for too long. If you poke a bear long enough, you're going to get bitten.