I may have given the impression that led to the conclusion that "His publishers wouldn't sign off on it" ... if I did the true answer is a bit more complicated.

Bantam wanted Dad to keep writing Westerns. They did make that clear whenever they could. But they did not out-and-out refuse to allow Louis to publish in other genres with other publishers ... they couldn't. Dad was sensitive to being successful in one genre and then failing in another, and failure would have been easy if his works were spread across a book store in several categories with his having no way to leverage his existing fans because they didn't know where to find his other work.

He was intelligent enough to take the advice of his publisher, but then try to turn his section of a bookstore into the "Louis L'Amour" section, rather than the "Western" section. This is all very "inside baseball" for the paperback book business of the 20th century but it wasn't like he wasn't allowed ... he could do what he wanted yet was smart enough to realize that, once established and successful, a move was harder to make. He did get push back from Bantam, but it wasn't something that would have stopped him if he hadn't recognized it's wisdom.