The writers of books, movies, and plays were educated people. They went to college. Scholarship in the '50s and '60s revealed that the Western was a kind of imperialist propaganda to sugarcoat the violent theft of the land and the murder of the indigenous population by the state. The writers learned too much about what really happened and couldn't keep up the charade. Propagandists usually believe the lies they tell, and the writers could no longer believe in the Western. For a while, they tried what ere called "revisionist Westerns," but audiences didn't like them and the genre slowly died. Some elements of the Western were adopted by other genres like the science fiction and superhero films. Instead of Tom Mix riding to the rescue on Tony the Wonder Horse, we now get Batman and the Batmobile.