I can't say, myself, since I don't recall black and white television broadcasts, let alone pre-tv radio days. I'd have to guess that people sat close by because the signal wasn't so great, in order to hear it better.
Sitting by the radio helps focus your attention and keep from being distracted as you move around doing things.
Even now while listening to talk radio, if an important segment or interview is coming on, I prefer to sit close to the source of the sound (the important part being "to sit")
" I'd have to guess that people sat close by because the signal wasn't so great, in order to hear it better."
Uh... That's why the volume knob was invented.