It doesn't, though. The hero's journey or "monomyth," a term I utterly HATE, is a specific type of narrative. It's a subset of the quest narrative. Yes, The Hobbit and The Lord of the Rings fall into this category. It requires the three act structure, which is also not universal.

For example, the courtship narrative, while it is sometimes incorporated into the hero's journey, is not the hero's journey and is the basis of the world's most popular genre: Romance. The courtship narrative is "Couple meets, couple is attracted to each other, some obstacle internal or external keeps them from getting together, they overcome the obstacle and mate." (It can be more than two people). I wrote a blog about how this is also the structure of the SF first contact narrative, also not the hero's journey.

Another classic narrative that does not fit that is extraordinarily popular is, of course, the murder mystery. In mysteries, the detective seldom HAS a character arc because they exist as an audience standin with whom you travel to solve the mystery. You can read the Poirot books in any order you want because while he is a wonderfully written character, he never actually *changes*.

While many SF/F classics DO fit the hero's journey...Tolkein has been mentioned, Star Wars is consciously based off of it, not all do. Dune, for example...if you think Paul Atreides is any kind of a hero, you're misunderstanding.

Campbell picked and chose myths to support his narrative.

And I should stop now before I write an entire post.