I disagree. I know I'm on the fringe but I make my living as a writer and 100% of my work is written in Markdown (MultiMarkdown, actually) that I then convert to HTML to paste into WordPress. Is it perfect for everyone, no, but for the subset of users who want to roll their own server setup and still have an easy-to-use publishing platform, it sure does fill a lot of boxes.
Moreover, I can teach people Markdown 10x faster than I can teach them CMS-specific HTML rules. Moreover, WordPress's TinyMCE stuff can break quiet easily (we have to disable it for most of our writers, I'm still allowed to have it because I never use it), so having a readably syntax AND having an instant-preview seems pretty perfect.
I'm another one who writes for a living and writes 100% in Markdown, then convert to HTML for Markdown. I just moved my own site to Kirby so I could publish with straight Markdown files. I know we're far from the only ones that do that.
You aren't alone. There is actually a version of Markdown for writing Screenplays. When writers adopt Markdown then I am not sure who Markdown is not for.
Markdown as I see it is for those who are trying to emphasise the text over style, which especially means writers. What it doesn't mean is random webforums where every second post has a rainbow of colours, boldings and so forth.
Moreover, I can teach people Markdown 10x faster than I can teach them CMS-specific HTML rules. Moreover, WordPress's TinyMCE stuff can break quiet easily (we have to disable it for most of our writers, I'm still allowed to have it because I never use it), so having a readably syntax AND having an instant-preview seems pretty perfect.