It doesn't. X was the only place I know of where that was a thing.
Because of scrolling on Thinkpad keyboards (using the middle click), I had to turn that feature of every time, especially while working on longer documents I would otherwise accidentally paste stuff at random places.
(It's not just macOS.)
From where I sit I have 5 Thinkpads set up within reach, and I have a few more in other rooms. They are by far my preferred laptop.
Most run Ubuntu as their default OS, most have the trackpad disabled because I usually use the trackpoint for everything, and on all of them I use middle-click to paste extensively.
The accidental pasting definitely kept happening to me, likely due to my bad habit of highlighting sections while to focus on them.
But hey! At least they are only flipping defaults, not removing the feature outright, like they did type-ahead search. [Insert angry rant here]
About your first point, however, keep in mind that "middle click insert" has been the default behavior in X since the 1980s, long before Windows or current generation MacOS's were around. To me, this is such a basic functionality, I would compare it something as fundamental as CTRL-X/C/V for cut/copy/paste on Windows.
As someone that habitually highlights what they are reading it was generally beyond useless for me. It was actively making me mad when I accidenatally pasted some non-sense because I just highlighted a paragraph before and accidentally inserted it into something.
Or in anything that's not X?
Speaking personally for me only, I don't think it's a great thing. The <however many> clipboards on Linux is... not really a great thing. I for one never know which of the buffers contain what. And this is compounded by the fact that selection may or may not overwrite what's in one of the buffers, and middle click may or may not paste whatever was in that buffer. Additionally compounded by how inconsistent the behavior is across apps.
I, for one, use the different clipboards concurrently all the time, with "highlight & middle-click" probably being the one I use most often. It's the most convenient for me most of the time:
- only two interactions (one drag & one click)
- completely mouse-based (no keyboard interaction necessary)
- hence only requires one hand (look, ma!)
Bo! Let's fight! And both get banned from HN :)