Why does Milhouse's dad hate him?

Only the people who make the show will truly know the answer. I personally think that it is because Milhouse is his wife's son as well. If that makes sense. Milhouse's dad has a terrible relationship with his wife. I think they got a divorce and I think he is showing that same hate to his child. There are people like that. Whether that is the case in this show I am not sure, that is just my opinion from what I noticed in other people lives. Hope that answers your question