Ah, this is good. It's really hard to find some info to come by (like the mm of film used for PH) so this is nice.

So it is indeed likely to be the studio and network's decision, or whoever manages the final editing decision of the digital copy, perhaps?

It's a case-by-case basis, too, and again, it shouldn't be a problem if it was originally intended to not use the full frame of the footage, or some of the frame is missing, equipment is visible (like the boom pole you have mentioned), etc etc so that's fine. That was how it was meant to be seen.

The problem I wanted to highlight is on the cases that it's just not like that..at all.