from the link:

CoffeeScript’s intent, however, was never to be a superset of JavaScript. One of the guiding principles of CoffeeScript has been simplicity: not just removing JavaScript’s “bad parts,” but providing a cleaner, terser syntax that uses less punctuation and enforces indentation, to make code easier to read and reason about. Increased clarity leads to increased quality, and fewer bugs. This benefit of CoffeeScript remains, even in an ES2015+ world.

so, it's not really about "CoffeeScript's functionality" but more it's "style".