Why do people tend to turn into horrible people when gaining positions of authority?

Unsure if this is the correct subreddit for this but I just find whenever a person I work with in my current job gets promoted or gains a position in which they’re to supervise/manage me and my other coworkers they always devolve into the nastiest assholes I know. Even a guy I was relatively good friends with got a supervisory position within our company and is now such a dick. Do other people find this?