Emacs is a full IDE, not just a quick one-off editor. Its power comes from having everything scriptable from the ground up. Contrast this with the modern Extension concept, where there is a hard line between the editor's code and any changes you might want to make to its behavior.

I think vim is probably similar, but I've not gotten into it that much.

Exactly, and infact vim is very simular, neovim in my case extensible through lua scripts as an example. It's as light or feature packed as I like.

Contrast that to Eclipse and Visual Studio (not vsCode) and it's clear why the larger IDE's are falling out of favour.