Because he believed his own hubris and thought he could get away with it. Like he did in 2014. Everyone expected Ukraine to fold and this all to be over within a couple of weeks. I sure did. But as it turns out Ukraine actually did have a backbone and they bent but did not break. Today they are better equipped than the invading orcs and are highly motivated as they are fighting for their survival. Regardless how this ends up Putin and Russia have lost and are accelerating Russia’s decline from a former world power to just another backwater authoritarian **** hole