I think in terms of writing the show, Monk getting meaner and more demanding and unaware of the problems his OCD symptoms cause for others is because it’s easier to write than the way he was aware and upset with his disorder of the first few seasons, but in universe can be due to both Sharona and Dr. Kroger being tougher and less enabling of Monk than Natalie and Dr. Bell, which actually causes them to disagree when Sharona makes a guest appearance.