I mostly listened to tech podcasts like talking machines and econ/business stuff like freakonomics or village global. They all mostly follow an interview format where the guest is only there to promote something that they work on.
They are there because they have insight into a phenomenon they have studied and is being discussed, and they may have a book or something that further explains what they are talking about should the listener be interested. Should they not mention or promote their work?
Almost always the main guest is there to primarily plug something. They almost are never there just to discuss some findings.