A lot of it, sadly, is more so that Putin is on a power trip and is too proud/arrogant to admit mistakes, problems, to pull out, and he's told so many lies, spun so much that all he can do is dig deeper as if he openly admits it, he's arrested journalists, attacked people and so on for telling the truth that he was trying to conceal, and covering up his own soldier's death's who he's using in a secret, unjustified war and so on, so if he says "sorry" he's just going to look terrible, and has to go deeper.
That. Plus, you know, the fact that he is winning. He sees a power vacuum and lack of resolve amongst of powers, and he steps in and does what he wants. I mean, sanctions? Ukrainian army? What and who is actually stopping him? He will continue to push until either someone big pushes back with actual force, he gets everything he wants, or he gets bored. He doesn't need to say he's sorry, because there is no one willing to punish him for his actions.
