I often enjoy movies that are unexpected and don't fit neatly into one established genre, but I think these tend to get lower audience ratings, while films that deliver to expectations do better, even if most of a randomly selected audience would dislike them. If a movie is a comedy, with a poster with big red letters and a white background, people know it's a certain kind of movie, and mostly those who enjoy those movies will go see it. Likewise with documentaries about some niche interest - those who watch it mostly sought it out because they're into that.