If most developers haven't heard of them, it's because most developers don't create design systems. Even when you use a design system, the actual use of design tokens would likely be hidden.
Material Design uses them. https://m3.material.io/foundations/design-tokens/overview
Fluent UI uses them. https://fluent2.microsoft.design/design-tokens
TDD, DDD, extreme programming etc come from the same observation: the client does not know their needs. Even if they do, those could change. So you want to build systems which are easy to change. And we still get thousands of pages published in the form of books or blog post for something written and explained in a book almost 50 years ago.
Not true. This kind of comment is exactly why most of us flock to this site. It's important to point out when the emperor wears no clothes. There's already an army of self-promotipn types forcing this nonsense onto everyone.
Yet who does things like that?
Web developers have tendency to do not innovate themselves, they need to be told by $tech_influencer that you can create your own custom solution
In C you'd maybe do it by prefixing all the relevant macros with DESIGN_foo but I think part of the goal of this is outlining all the potential "Foo"s and utilizing it to maintain consistency across a large organization