IMO it's no more complicated than Putin having expected extraordinary personal benefits.
If Kyiv had succumbed in days, and the government were replaced by a subordinate one, his power in the region and in Russia would have been immensely enhanced.
Ever since that miserably failed, the military and propaganda war appears aimed at rescuing, as much as possible, Putins position.
Any further explanations contributed by that seasoned liar are to be taken as inconsequential.