He made it because he predicted that it will have some effects enjoyable to him. Without knowing David Lynch personally I can assume that he made it because he predicted other people will like it. Although of course, it might have been some other goal. But unless he was completely unlike anyone I've ever met, it's safe to assume that before he started he had a picture of a world with Mullholland Drive existing in it that is somehow better than the current world without. He might or might not have been aware of it though.
Anyway, that's too much analysis of Mr. Lynch. The implicit question is how soon an AI will be able to make a movie that you, AIPedant, will enjoy as much as you've enjoyed Mulholland Drive. And I stand that how similar AI is to human intelligence or how much "true understanding" it has is completely irrelevant to answering that question.