I don’t know if it’s still a thing in the digital age, but having even just a few seconds of dead air back in the analogue broadcast days could mean that “silence detectors” all over the country would start going off and radio engineers everywhere would think there was some kind of problem with their station. So there had to be talking, music, something at pretty much all times.
If you wanted intentional silence you could play comfort noise in the background.
Jeremy Brett is my favorite Sherlock. It’s like David Suchet and Poirot, he just nails it.