Because very few people actually care about the things that emacs has to offer.

Tools like VS Code do the job well enough for the majority of people, with just enough configurability and much greater ease-of-use.

Emacs has a similar problem to Lisp: Infinite configurability and expandability (plus the lack of a "blessed set" standard that people actually like enough to use out-of-the-box) means that everyone's environment and tooling ends up becoming incompatible with each other.