Most users know how to muddle through with WYSIWYG, but they also lack experience with actually reliable editing environments. So they just take for granted all of the fighting they have to do with the semi-hidden state of the WYSIWYG editor.
99% of WYSIWYG users also fail to use their word processors correctly even on the terms of those word processors themselves. They most often totally eschew templates and page/paragraph/character styles in favor of manual formatting changes that all individually 'look right', turning all sizeable documents into unmanageable messes when it comes to consistency or formatting changes. It would be generous to describe this norm as actual proficiency, especially in a professional context.
Moreover, it's clear that the WYSIWYG paradigm itself is what invites this widespread incompetency and poor document quality. Why manage things in a systematic, organized, or efficient way when you can watch the document take shape before your eyes by highlighting individual words and manipulating their appearance or padding things with spaces, without having to give a thought to the structure of your document in advance?
> Markdown seems an nice, limited format that would make for a nicer, saner WYSIWYG for developers (except the inline HTML part of the spec).
WYSIWYG is not in fact less buggy with Markdown, as can be witnessed in the unholy WYSIWYG-Markdown unions of, e.g., Teams and Slack. You still inevitably end up fighting the system just to get your cursor to stop adding text with that formatting, or to escape that quote box, or whatever.
