Why doesn't my father understand how bad my old manager was?

Several years ago I had this awful boss. When he first started he made himself seem like a fun loving boss to work with. As time went on that all changed. He would breathe down the necks of the leads of each department. He would also give some of the staff special treatment and have them do other work while he would breathe down the necks of staff that had disabilities. I did tell my father about all this and he still liked the manager. I told my father that he hasn't seen my old boss's true colors. Now why can't he seem to understand how bad he was?