The purpose of tokens is be able to have a single language-agnostic source of truth for the core bits of the design decisions.
Let's say you have a website, an iOS app, an Android app, Figma templates, and documentation. Let's also say your main brand color is currently a certain shade of green.
When your brand evolves to a different shade of green, you update one value in one place. All of the above surfaces are updated at the same time.
This was not a thing with Bootstrap, and it's not a thing with CSS variables and derived values. This is an organizational tool that increases in value as a multi-platform company grows.
It's true that most websites and apps probably don't work this way today. I've worked in a lot of them, and they were not pleasant developer experiences burning up way more developer time than necessary. They become unwieldy at any kind of scale, producing all kinds of visual bugs and incongruencies on every single engineer PR.
An interesting question would be: "how much does it matter that the visual language is consistent across a company's assets?". But the answer to the question of the utility of the design tokens is obvious if you do decide that design systems are important for a business.