An Ordinary Mind on an Ordinary Day

Why conscious thought as described in the article was thought to be signs of a delirious person was because that’s where you could find it in real life, is my guess. If someone blabbing about without a listener, they’re insane. So to describe someone’s inner thought would render them insane to the reader. But with psychology came greater understanding and value of the inner thoughts and now a character no longer was deemed insane by having innate thoughts.