On TOTN the guests as well as the audience are both listening and talking. TV is passive by contrast. The audience can only watch. The guests are limited to short responses to the host. On TOTN the guests are there with the host with equal access to the microphone.
Listeners become part of the show.
And Talk of the Nation requires a depth of knowledge because we stay with one subject for an hour. The sound bite is a TV concept. It works in the context of a very limited discussion. On radio the pithy sound bite comes across as thin, even silly. And you can bet it will be given a rough going over to expose the weaknesses in the argument behind the sound bite.