[icey]

That's only true if you want someone to watch a movie exactly once and not think about it again.

Sowing confusion creates a ton of follow-on merchandising opportunities in the form of special editions, additional cuts (directors cuts, unrated cuts, extended editions), explanatory books, etc because the people who enjoyed the movie will want to continue to learn more about it.

That kind of narrative vagueness allows people to fill in the missing bits with their imagination, which is a very powerful way to get people to like something.