Between novels and short stories, Stephen King has published hundreds of stories in the 40 years since his first novel,
In August of 2016, the author submitted paperwork to terminate his rights agreements with studios that held the rights to The Dead Zone, Cujo, Creepshow, Firestarter, Cat's Eye, and Children of the Corn. According to the paperwork, the process takes nearly two years to be finalized, after which the rights holder would have five years to bequeath them back to King.
One interpretation of this paperwork is that King is sick of lackluster products taking advantage of his titles, like the straight-to-video Creepshow 3 or a slew of underwhelming Children of the Corn films. Since King won't be granted the rights until September 1, 2018, and having to potentially wait until 2023 to wholly own the rights, merely preventing more stories from capitalizing on his brand would make sense.
Another interpretation is that King himself wants to become active with bringing some of his more popular stories back to life for new adaptations. While there are already dozens of adaptations of his works, a large majority of them fail to capture what makes the original stories so compelling. This year's The Dark Tower adaptation was a box office and critical failure, but early reviews of September's It are strongly positive, potentially putting it in a place to break box office records.
Between the early word on It and opportunities existing with a variety of streaming services, King could be looking to expand his empire even further.
Bloody Disgusting also reports that remakes of both Firestarter and Cujo are already in development, with the recent legal proceedings forcing the productions to expedite the process before losing their opportunity completely.