What makes you say that? How do you know that Mr. King has not been writing his own work for 20 years, and who is writing it? Tabitha?
Twenty years ago is seven years before his “career-ending” accident. What happened to him 20 years ago?
Perhaps longer, doubt it has anything to do with family but more to do with being owned by the publishing co.
My opinion, of course, but I have noticed interesting things about “established” writers and publishers.
In the paperback vs. hardback “Stand”, different brand candy wrappers were left behind by Harold....
Carolyn Keene, Victor Appleton and Franklin W. Dixen turned out to be “Staff” after 50 or so years, and Grossett and Dunlop has changed names several times.
I think the “best” writers with many publications only need to submit outlines or the first couple of chapters to the publishers, who have “Staff” flesh out the rest.