It was only with the death of the pulp magazines that he committed full time to Western paperback originals ... and he never expected to get stuck there. He started trying to break out around '58 or so but couldn't see how to do it without restarting his career from zero (like with a new publisher).

By then he was married and not ready to take unneeded risks. It was only in the 1970s that he began to sneak other sorts of material in under the guise of "frontier" fiction and then graduated to full fledged writing in other genres in the 1980s. It is noteworthy that The Walking Drum was originally written in 1960, yet only published in the mid '80s.