King has been asked. Numerous times. From all over the industry. That's very different from Rowling, who hadn't been asked, and who has already given attraction rights to a theme park.
King has been burned by adaptions a few times (most famously The Shining). And haunts are notoriously hit-or-miss. It's entirely his prerogative to avoid that from happening again.
Now, if anyone could convince King to give up haunt rights it would be Universal. Ironically, because of Rowling.