Well, maybe not a lot on the "why" (writers are supposed to get out there and promote for the publishers) but here's some on the "how." If you're interested in the fun details of national media, read on!
Preparing: Generally I get a notebook together of sticky notes, organized with different subjects on specific pages, and that's my briefing book to study beforehand. I have no script; it's just responding to questions from the director, who sits alongside the camera and reminds me "don't look at the camera - look at me!". TV directors want short vivid quotes (each 5-7 seconds or less) that they can clip from a full interview tape, to go along with the narration and the video. That can take several hours of interviewing, so they're not using much! Most interviews put me in a chair, though I much prefer walking around. But that's harder to shoot and to maintain continuity so that doesn't happen often.
NPR's All Things Considered: that was a 20-minute interview about my article for Smithsonian on the shenanigans of early congressmen. They set up the interview in the basement of Central Lutheran Church in Minneapolis, I guess because Minn Public Radio's studios were booked. I was on the phone with one of the hosts, and it was recorded for later broadcast that Thanksgiving weekend.
NPR's Kojo Nnamdi Show: They got in touch through Harper's publicist, and set it up for DC when I was there on a book tour. Location was the WAMU-FM studios. A professional setup, complete with “green room” to get ready. Host was Frank Stasio, now at North Carolina public radio. He had actually read Inviting Disaster and had a lot of good questions, and listener calls. Got a picture of that. The audio is here.
TV networks: Cable TV usually hires an outside production company to do everything, after being hired by the network. The network has an exec, the showrunner, to keep tabs on the show and the budget. He or she has a final say over how it turns out, using memos called “notes” to have the prodco make changes to the rough cut.
CBS's Charlie Rose show: for an article I did about how buildings would age if abandoned. This was at the CBS studio in NYC, late at night. Had a limo driver for that one.
National Geographic Channel: Production company was out of London, Darling Smithson, doing a final show for the “Seconds from Disaster” series, on the Challenger loss. I met them in Wichita and we shot the footage at the university and at a space museum in Hutchinson KS. A larger than average crew for cable TV: six people, because they were shooting some scenes at the museum to recreate the cockpit and the commission meeting.
History Channel: because I've done over a dozen shows on a variety of series, these have been shot all over the place, from my living room, somebody's house overlooking a canyon in LA, overlooking the collapsed 35W bridge, the NYC waterfront for the Inviting Disaster series, various hotel meeting rooms and studios, and a steady rain in Toronto for the "Life After People" series. THC has a tight budget so typically in the field this is a crew of three: director-writer, a camera person, and a sound person. (David DeVries was the director on Inviting Disaster, and when we were taking a ferryboat over to Manhattan the wind was so strong it whipped the glasses right off his head, so he had to work the rest of the day without them.) Occasionally the production company adds one or two for lighting or to handle production details. Everything and everybody fits in an SUV. Learned that in NYC, the camera SUVs have steel cages to safeguard the camera equipment in the back, which works except in the case of thieves carrying thermoses of liquid nitrogen. Key role for the sound guy is to make sure there aren't distracting noises in the background. One interview was interrupted several times because of a parrot nearby, calling from a window well.
Clear Channel's Coast to Coast AM: They insist on a land line: no VOIP, no cellphone. These interviews (mostly with Ian Punnett, all live) have been as short as 10 minutes or as long as three hours.