While some people certainly are motivated by interest in doing pure research, I don't think that's the dominant factor. From my anecdotal experience, far more

While some people certainly are motivated by interest in doing pure research, I don't think that's the dominant factor. From my anecdotal experience, far more are turning to PhDs simply as a way to avoid the brutal job market. They're choosing it for financial reasons, even though their reasons are backed by faulty information.