It's a part of the evolution of television. A notion that someone sitting behind a desk can be seen as an authority figure 'lecturing' instead of imparting information.
It has reached ludicrous proportions with the Channel 5 News - they either have to perch on benches so uncomfortable and ugly that no sane person would contemplate going near them, or else they are standing leaning against a piece of set half-way up the studio wall, appearing to have been caught short nipping to the loo!