those are layout grids and not grid layout (huge difference!)

You're right, I used a wrong link, fixed now. So Figma has both.

now to get designers to actually use these things.

Figma has a bunch of good tooling, but getting designers to use it, and use it consistently, is the real problem.

Designers exist in a realm seemingly, where outside pressure can't really be put on it from an organizational level to get them to uniformly adopt a set of standards they will always adhere to. Every company I have worked at, big, medium, small, seems to have this problem

To me, things like mobile-first responsive design and grid-based graphic design thinking are core components of designing for the web, so it's a bit wild to me that Figma, with such popularity, is just now getting grids, and as far as I'm aware no GUI tool has ever succeeded at building a capable visual responsive design tool close to on-par with just designing in the browser.

This does not seem that surprising to me.

Browsers are by and large black boxes—less because of their architecture and more because of the sheer size of the code, although Firefox, for example, seems to have been moving towards a less open architecture for most of its history as well (deCOMtamination, death of XULRunner, Quantum, etc.).

What you really want in a parametric web design tool is to crack open the layout engine and the CSS cascade and inheritance, at the very least. That’s a lot of work to target a demographic of designers and programmers who by now have largely decided to ignore CSS in favour of reinventing inline styles badly (Tailwind) and insert markup as necessary for the desired visual effect. (Is there a tool to do CSS in terms of React/etc. components, with proper cascading, custom pseudoclasses and pseudoelements and so on? I haven’t seen one.)