The "just stories" employ the publishing, television, film, and video game industries (plus ancillary industries that support them). I can't even venture a guess as to how many thousands upon thousands of people feed their families on "just stories".
The reason why canon matters is because it presents a single, unified creative direction for the fiction. In a world where canon does not matter anybody creating an unsanctioned work can steer the fiction in an unsustainable or downright bad direction, literally taking the food out of the mouths of families.
Distinguishing between official and unofficial narratives keeps the responsibility (and the risk) in the hands of the people who staked their livelihoods on it succeeding. Taking that control away from them just so people respect some lonely teenager's shitty fan fiction is unconscionable.
Again, it's real money people pay to experience fictional stories. If you don't understand that... I don't know what I can do for you.