Mike comes very close to the real story here. There's people posting one fake trailer per day, and if their output becomes indistinguishable from a real trailer... why not make a whole movie? Yeah yeah yeah, presumably starting with knockoff clickbait trash, written by a robot, starring actors who will sue them into the dirt. But there's no technical separation between that, and making shit up from scratch.
Any film student with a thousand bucks and a first-draft script can edit together an "animatic" that's basically a finished film. It's like their stock-footage library had exactly what they wanted, every time.
Or they can hire actors like normal, to give real performances, and have the robot make up a billion dollars in CGI.
This does not go well for studios.