With a really good design team, this isn't a problem, as the numbers are just pointing to something in a design document, but I've yet to see something that well done in the wild. And its not really that hard to make such a design system using css or preprocessor variables
Does it matter? Putting aside that anecdotally it seems very rare to override the default values for spacing anyway, m-2 is twice as much as m-1, which is whatever the baseline spacing for your project is.
Sure it can vary from project to project (though again, it doesn't seem awfully common for folks to do), but the config file is in your source control so m-2 is always consistent for the project you're working on.
Of course there is a big group of devs who use tailwind for easy copy paste templates that never change the config. But those who use as system use config a lot.
So anyone using Tailwind already has the setup to add tailwind.config.js into their project. They make it as easy as it can possibly be.
The reason why people don't change the config is that you need the default tailwind config for all the copy-paste-able snippets to work. People buy something like TailwindUI and copy what they find around. Including things like colors (which i find super stupid that the TailwindUI team didn't you know... use their own config OR css variables to be able to change brand colors).
And that kind of usage of Tailwind is lazy and you won't learn anything. But that's up to people. It doesn't mean Tailwind is bad abstraction or not possible to use for efficient design systems.
Even if I don’t know what specific values m-2 may hold for a given project, I certainly know a lot more about it right off the bat than whatever .class-name you may have come up with from scratch, and can reference the config to know the rest.