People are doing it, but not that much, because while it generates some pretty good five-second scenes, it fails terribly at generating any long-form video. And by long-form, I mean 'longer than 30 seconds'.

I think what people want is to tell a story that's in their imagination, and no current AI is up to that task (at least in video format). Great for making an animated PNG for a meme, but not for adapting that fanfic you are writing.