I don't do front end these days and don't really have a dog in this fight, but most code is nouns and verbs, while design choices are adjectives and adverbs. When the business decides that we need to run, not walk, you can just change the name of the function from walk to run instead while changing the code, if that seems appropriate. With CSS selectors, when the business decides we need to change the "feel" of the page from "spiky" to "gentle," you might only want to change some subset of the design that was built up around the "spiky" concept, while leaving others as they are. There is not a comprehensiveness and absoluteness to the changes, and it's a lot harder to reason about "pure functions".

Add to this that CSS is like a codebase built on try/catch and throwing errors for its primary control flow mechanism, where the only thing that tames this is the naming conventions employed, and you've got a situation where the names really matter in a way that they don't when we're doing other programming, because the names are the only connective tissue to help you reason about the "control flow" once your css starts getting complex.