I haven't personally used VS Code much, but from what I understand, it still runs in two castes that don't, generally, mix: there's its core code, and then there's plugins, and the latter exists on a separate plane from the former. You can't write a plugin that redefines some core behaviour. The functions internal to the core are not all automatically accessible for any plugin. Plugins don't become fully integrated with the core code to the point where the source file location is your only hint as to whether behaviour comes from a plugin or core functionality.

(A non-Emacs user might very well go "Emacs plugins can do what now?" at the description of a plugin re-defining a core function. That's a fully understandable reaction. That level of hackability is not for everyone. But as far as I can tell, it's unique to Emacs and very small set of other software.)

But I could be misunderstanding this. Maybe VS Code actually does have Emacs-level hackability, in which case I'd probably want to try it out more than I have!