Presumably the full name (e.g. 'Joe Bloggs', rather than just 'Joe') is repeatedly used by interviewers so that people who turn on late (or who simply missed the introductions) will be able to work out who it is that's speaking.
Incidentally, I attended a school where the pupils were all known by their surnames and the staff referred to each other in the same way. (e.g. one teacher, seeking another, might enquire of a third, "I say, Smith, have you seen Forsyth today?"). That was in a traditional boys' grammar school in the 1960's.
However, by the time I was teaching in a Sheffield comprehensive school (1975-90), there was no greater way to offend a male pupil than to refer to him solely by his surname. I could, say, refer to someone called Michael Smith as Michael, Mike, Mikey, Michael Smith, Sunshine, Laddy, 'You boy' or by any of the many nicknames his friends had for him (even offensive ones!), without any problems. If I addressed him simply as 'Smith' his mates would probably have to hold him back to prevent him taking a swing at me. That was true of the even the most charming, well-behaved and helpful boys. The one thing that was totally unacceptable to them was to be addressed by their surname. (As far as they were concerned, it was more offensive than being addressed with a lengthy sequence of 'four letter words'!).
Chris