Putin made a lot of mistakes in this war. That they are fighting Ukraine with a 0.8/9-to-1 troops ratio is just one of them.I think you answered your own question. I don't know much about Ukrainians but frankly, I don't think Putin should have said in his infamous speech "Russia (Soviet) is responsible for the creation of Modern Ukraine" and questioning the country's current statehood. This became a war of national identity for Ukrainians. That's a pretty strong ideological reason to fight.
Only a military genius would invade in such a way