Also, it's kind of right there in the name. "Org Mode". It's not just a markup format, it's an emacs mode.
My org files quickly accumulate custom elisp snippets for automating small one-off things like rendering embedded dot with Graphviz and displaying them inline. I don't think I'm alone in that. Unfortunately, that creates a situation where, whenever I try to work with org files in other editors, there's a certain "it's like opening Photoshop files in MS Paint" aspect to the experience. Too many things that I've come to take for granted about how I'd interact with and edit these files no longer works.
Markdown, on the other hand, is just a markup format. It has lots of dialects, but it isn't really owned by anyone. That creates a very different power structure: Markdown editors are free to just try to make a good Markdown editing/viewing experience, whatever that means to that particular editor's developer. There's no looming and inevitably unfavorable comparison to the format's native editor to have to contend with.
Markdown supports HTML (with JS), and HTML/JS is quite powerful. I can make complex computations and drawings with JS libraries, then present them nicely with custom CSS. Some markdown editors supports embedded HTML/JS in preview, which makes them easy to use as IDE. My favorite editor is Marker[0].
I suspect that I can write embedable applications in JS and load them as libraries in Markdown to perform advanced stunts, like in Org mode.
Except it's not just a markup format. When connecting it to the agenda system in emacs you end up with emacs lisp snippets (easily, not always) in your org files. And that's just part of the basic usage:
%%(org-anniversary 2021 11 18) It's been %d years since the 50,000th org-mode thread on HN.
Or with org-babel you can have different blocks of code interact with and reference each other:
Completely agree. I think there's a continuity between the misconception of Org Mode as being just being another markup format and Emacs being just another text editor.
Because it's so integrated with Emacs, and all other editors are second class citizens (/hosts)?