It’s more obvious that simple writing is linear like a thread, and needs a “story,” whether or not it’s fiction. The process of writing is not linear, but reading it will be.
It’s easy to forget with more complicated technique, while trying to keep careful and precise track of many threads (thus most philosophical writing lacks direction). Even a woven tapestry needs to depict a story to bring threads together.
Whether narratives, themes, or some other suggestion of linear direction provides that sense of “story” to carry through, it’s most important with a very complicated and challenging piece of writing.