Correct me, but I can tell what 16px is, not 1rem. 1rem can be 16px, 18px, 2000px. When you see tons of relative units, you need to doble check what it's going on. With pixels you see explicit values, so no double checkings.

Yes, but a typical change request would be something like "make this menu font size larger", and in this case having menu independent from other parts of the page is better. Also, if you build a framework with variables, dependence on root font size, it would be complicated and most devs won't like to spend time learning it and thinking how to solve their task within it. Simple is better here.

> I also find sites that do everything in rem/em more assessable as the padding also scales if they have a increased font size due to low vision.

If you use Ctrl +/Ctrl - for zoom, then everything scales proportionally regardless of whether you use pixels or rems. You are trying to solve the problem that has been already solved by Opera, and later by other browsers more than 10 years ago.

> Also, hardcoding things instead of using variables makes things harder to maintain.

In my experience, it is the opposite: simple code without implicit dependencies is better. Because the typical task would be to change one part of the page without affecting other parts. With a simple code, I would use DevTools to change the CSS rules and then I would move the changes manually into CSS file. But if the site uses some complicated framework with variables and rems, I will have to spend time learning it, see where is a variable defined, what can be affected if I change it, etc. It just takes more time and nobody of the devs will want to learn your custom-made CSS framework.

> padding also scales if they have a increased font size due to low vision.

rem: automatic for the people

IIRC the standard pixel was always divorced from the real pixel. Or at least for a very long time.