I think you might have missed the word "especially" before "prepared" in the post you're replying to. The language is also a bit ambiguous (see below). It's we

I think you might have missed the word "especially" before "prepared" in the post you're replying to. The language is also a bit ambiguous (see below). It's well known that guest are (usually) prepared (by the show!) in the sense that they at the very least have a general idea of the major points of conversation, but having a full list of all the exact questions, etc. is quite a bit rarer (AFAIK, at least). Regardless, the parent poster could also have meant that the guests themselves(!) do very little preparation with the information they get from the show. The amount of preparation by the guest would probably depend heavily on the agent, the contentiousness of the questions that they know about, how high the stakes are (e.g. first ever interview on Colbert for an up-and-comer?), etc. etc.