Death of the Author is, in its essence, the way literary criticism can exists at all as an academic pursuit.

It's not a way to say "my interpretation is right because subjectivity is king" it's "we can only go so far in studying a work of art based off the biographies of artists and half-baked psychological analysis. so lets use the other resources we have available to us to make this a meaningful venture in the long run". That, whatever one's intent is they can't purely reproduce it within a text, because writing is an art which has its own rules and conventions and even words themselves are barriers on expressing thoughts with ideal perfection. That it is, ultimately, easier to compare texts to one another in their own kind of microcosm, one where we see countless similarities in styles, reference points, structure, and concepts -- no book is an island onto itself. Rather than comparing actual people, who we can't psychically glean information from and are not trained to do as literary critics -- especially if said author has literally died or we have no Earthly idea who they actually are. To be a study of literature, as it were.

Death of the Author being appropriated for arguments in fandoms and casual forum discussions where it's widely misinterpreted to mean whatever you want has given it a waxy coating of self-indulgence. Which I guess it would be ironic, except it's not poetics or prose fiction, it's an essay with a formal argument - made pretty well, it convinced me - that just got reduced to a meme.