proprietary
Well related to the owner is the very definition of proprietary. So as far as upstream vs not available for upstream is concerned. That is what the term is used for in linux.
So yep by its very definition while a manufacture is using a licence that other distributions cannot embed with their code. Marking it proprietary is how the linux kernal tree was designed to handle it.
EDIT: The confusion sorta comes from the whole history of IBM and the PC.
Huge amounts of PC hardware (and honestly all modern electronics) are protected by hardware patients. Its inbuilt into the very history of IBMs bios being reverse engineered in the 1980s.
So as Linux for all its huge hardware support base today. It was originally designed as a x86(IBM PC) compatible version of Unix.
As such when Stallman created GPL 3 in part as a way of trying to end hardware patients. Linux was forced to remain on GPL 2 simply because it is unable to exist under GPL 3 freedom orientated restrictions.
The proprietary title is not seen as an insult. But simply an indication that it is not in the control of the developers labelling it.
Only if those device makers are willing to use it. And that has always been the tightrope linux has walked.
Its very history as a x86 platform means it has needed to develop drivers where hardware providers did not care. So that code needed to run on closed hardware.
It was bloody rare in the early days that any manufacturer cared to help. And still today its a case of rare hardware that needs no non free firmware.
Free hardware is something I’ll support. But it is stallman et als fight not the linux kernel developers. They started out having to deal with patented hardware before any one cared.