I think it may be because of the teacher / student power dynamic. I expect you get used to treating everyone like they're much younger than you and that you can treat them disrespectfully without any major consequences.
My limited experience with academia is that professors are thrust into a position of power with very little management training, experience, or support. Additionally, research professors may have no pedagogical skill and yet they are expected to both research and teach to some degree. This is a recipe for dysfunctional organizations and relationships.
And as the professor ages their best research may be behind them, and the ones who can't take a bitter pill like that may start punching down on people below them.
