Filmmakers aren’t like normal business people. Marketing a movie is not considered part of the normal day-to-day process. But in other industries, marketing is just an aspect of business. This makes a lot of sense. In the old days, your success as filmmaker depended on your ability to create an unproven product. And if your product (or in this case, your movie) did well with audiences, it was picked up, marketed and sold.
A long time ago, I worked on a short movie with a guy. Long story short, I found out the guy was being untruthful about money. He had hired one of my friends to build our movie website. When confronted, he told me some sort of story that was completely stupid and untruthful. Because he was a “friend,” I gave him the benefit of belief and dropped the subject.