Why does Charley say, he (Sam) certainly can’t go back to his old business?

Charley knew that though it was less profitable, the quiet business of hay, feed and grain would give Sam a greater sense of satisfaction. Moreover, being a psychiatrist he had no scope of reverting to his own profession as in 1894, a psychiatrist would be absolutely unacceptable, since in 1894 the science of psychiatry was in its infancy.