* I sometimes view on or want to share documents over sites like Github/Gitlab. If I share Markdown or even usually AsciiDoc, then the document is formatted appropriately even for people who are used to Word and rendered HTML. EDIT: Apparently this has changed since I last looked. Good news!
* I often edit from mobile devices, which almost certainly have no support for Org features. EDIT: There are apparently good org-specific editors.
* My desktop editor of choice is not and likely never will be emacs, so even with plugins that support Org it's always a hampered experience relative to what the format claims to offer.
It looks like it does everything I want and more, with all the little helpers you need overtop a plaintext format that's decent enough to read on its own. But I'm not changing my text editor just to use a single different format.
So instead I opt for the worst of all worlds and just use Markdown for everything because it's supported everywhere. It gets me headers, lists, code blocks, and sometimes checkboxes, and the rest I can handle ad-hoc.
EDIT: 5 responses in ~10 minutes, but 0 or neutral upvotes. I knew mentioning an editor preference was a mistake. Yes I have tried emacs for an extended period, yes I respect it, no I am not likely to use it myself.