Harry Potter is one of my favorite movies. I think it's so popular because it's beyond of people's regular imagination. The concept of the movie is new and fresh to people so many get curious about it and want to watch it more.
But why wouldn't it be Filch? He had Mrs. Norris and she was a remarkable cat. Maybe that's why he's so grumpy now. Too many people bringing owls and rules about cats so that there's nothing for him to do