Watching movie is a way to relax. It will be more relaxing to watch them in a confortable place. For example, I used to watching a good movies after a hard work. I set up a personal theater in my house. Since it's personal, I can choose a huge, soft sofa so that I can completely lie down and relax myself. On the other hand, it��s uncomfortable to sit in the movie theaters since the chairs are too small and the space allowing to stretch is limited. In addition, I also used to eat something when I watch movies. It is not a problem if I watch movies at home. In contrast, most movie theaters don't allow people to eat there. Therefore, it's way more confortable to watch movies at home.
Exchange opinions with friends making the movies more interesting. For example, if I see a interesting thing, I love to share it with my friends because they will laugh with me. There happy reactions make me feel that thing is more interesting. If we watch movies in my house, we can make comments and laugh together freely without worrying other people. However, there is no such freedom if we watch movies in the movie theater, that limitation will decrease the joy of watching movies.
Of course, there is an argument to be made for other positions. Nevertheless, for the reasons I have presented above, I think my opinion is the most valid.