Design tokens are an API
A hex value in a page stylesheet is a fact nobody can change. A token is a promise that the value can move.
When a colour is written directly into a page, that page stops taking part in the design system. The value is now a local fact. Change the brand colour and you must find every copy of it by hand.
Names, not numbers
A token gives the value a name and a job. --color-action is not a shade of amber. It is the colour that things you can click are painted with. The shade can change; the job cannot.
This matters more when an agent writes the CSS. An agent asked for a hex value will produce a plausible one, and it will be slightly wrong every time. An agent asked for a token name either finds it or does not.
The contract
Delta keeps tokens in one file and reads them back through the same interface that writes them. Pages consume the names. Nothing downstream needs to know the numbers. That is the whole idea, and it is the reason a retune of the type scale does not require touching a single page.