Articles about Org mode almost always make the point that Org documents are plain text and can be edited with any editor. That's true and it's part of what gives Org its power.
On the other hand, just because you can edit Org mode documents with any editor doesn't mean you should or would. Who, other than in an emergency, would do such a thing1? One reason not to do so is, of course, that Org mode runs in the Emacs lisp interpreter so you can't get agendas, generate reports, use the spreadsheet functionality, or a host of other things in other editors.
A more subtle reason, though, is that the Org language is integrated with the Emacs editor.
(Via Emacs - Irreal)
I agree … but …
I don't have a universal Emacs device. I use Orgzly on Android [F-Droid & Google Play] and beorg on iOS for tasks and agenda stuff when I'm mobile which fill the gaps a bit. I use Termux on Android [F-Droid & Google Play] for a more full-featured Emacs experience. And of course I have Emacs on my MacBook Air, my MacMini, and my Surface Pro 4.
There is a capture gap that still needs addressing. Then, manipulating that which has been captured.
I don't have a good solution, but I know that this is not (directly) an Emacs issue. And it should not be a Gnu Emacs issue, because RMS won't let it be. Too many compromises would need to be made in order to facilitate an "official" macOS Share Sheet for Emacs, for example.