But this isn't an isolated thing. Thor is a Marvel superhero, Disney's Hercules won four Annie awards in 1997, and any kid in the 2000s who was into trading card games could tell you that Yu-Gi-Oh! superficially claimed to have an ancient Egyptian theme. The integrity of the original material in all of these is patchy at best, but they stick in our imagination, anyway. They're just grounded in pre-existing narratives enough to be vaguely familiar, and therefore meaningful. No matter how much Arthurian scholars writhe at A Kid in King Arthur's Court.
I think we can look at Sherlock Holmes to see this kind of thing in action again. Sherlock Holmes is the fictional character who has been portrayed by the greatest number of actors. There's been dozens of TV shows, from Cushing to Brett, to now Cumberbach. There's been movies to suit every generation, the most recent featuring a garrulous Robert Downey Jr. There's been Japanese anime series, from Sherlock Hound, several episodes of which were directed by Hayao Miyazaki, and Case Closed, with a protagonist inspired by Doyle's tales. There's been western animation: Disney's The Great Mouse Detective, and a DIC series Sherlock Holmes in the 22nd Century. This is to say nothing of the vast library of literary Sherlockania stretching back even to before the ink was dry on half of Doyle's original serials. Star Trek was on Sherlock, too, giving us the lovely image of Lieutenant Commander Data in a deerstalker hat.
I think it is safe to say that humans will repeat what they like, and things become part of our mythology because we like them.
This raises another interesting connection, however: what is the difference between these adaptations, and the much-mocked, lowly fan fiction story.
I would argue that all of these things are actually fan fiction, too. Only that money has gone into their making, that they have been published and so are accessible and therefore respectable to audiences to consume, and that Sherlock Holmes and mythological sources are in the public domain and therefore there is no issue of copyright.
But fan fiction's a post (or series of posts, or a series of series of posts!) in of itself. For now, we'll content ourselves with the fact that in several hundred years there probably will be rampant and unchecked retellings of Star Wars and Titanic. We will probably be very happy we didn't live to see them.