Same as with music theory, writing, programming, or other creative endeavors or art. The thing is that when someone creates something from their heart, from an incredible desire to create and share their vision or experience, it often ends up following some kind of storytelling guideline. And that is because stories worth listening to have a structure that makes them engaging.

The problem comes in when someone tries to analyse the structure of stories and assume that they can create a template for telling new stories. If you start with the template (or the music theory, or the best practices) you end up with something that feels formulaic and like crap.

Theories of art are always descriptive and inductive, not proscriptive or deductive.