For the same reason people in infomercials seem to find it so impossible to perform basic human tasks like pouring a drink without a special drink pouring handle. The whole show is staged to get you to buy something, usually a movie ticket or a book. Talk show questions are often given to guests ahead of time to consider answers or given to the host by the guest to make it easier for them to promote their product. Neither of them is speaking as themselves, but as improv actors in an unscripted commercial.