In all seriousness, HTML started out as a markup language for documents. That is why tags like <p> for paragraphs and <b> for boldness etc. are so prominent.
If you aren't trying to build a SPA or something like that and you just want to mark up some text for formatted output ... HTML is kinda made for that task.
That being said, I tend to stick with Markdown since I find angle bracket tags to be noisy and distracting when I view documents in plain text.
It’s just plain old dumb boring static text that is being moved around the web.
The internet was essentially created so that CERN could share plain old text documents with others remotely.
Why do I need a big bloated overly complicated PHP webserver that talks to an overly complicated database, when it’s just plain old static text after all?
AsciiDoc still has no footnotes, but only endnotes. Therefore not really useful for writing non-fiction books. As org-mode files are only text files, you can use any editor you like. If you want all the goodies (agenda, TODOs etc), you have to use Emacs, yes.
Markdown is a formalization of formatting conventions that people were using well before it was invented as a separate product. It was slightly different - the link syntax was novel, and asterisks usually meant bold instead of italics - but it was close enough that the allure of 'your reflexes still work' held. Nothing else is as popular as Markdown because it isn't actually Markdown that's popular, it's what preceded it.
Personally I'm happy for it because it'll finally stop programming languages from inventing their own domain-specific oddly-syntaxed subset of HTML; the way Rust uses it is something others have no reason not to copy. For your own technical writing, AsciiDoc works pretty well.
I think markdown's popularity comes from its simplicity. For things like bulleted lists, especially nested ones, I can just type an asterisk and keep going. The raw input is still very readable (for the most part) and adding formatting is quick and easy. For anything basic - such as chat systems, social media posts/comments, or quick note systems - I don't think anything more is needed.
Something like reStructuredText (.rst) is a similar alternative, but I think that if you're irritated by the limits of Markdown then rST isn't going to be any better. If you really want good formatting options, then LaTeX is the best I can think of at the moment.
Imho Markdown is a overall terrible and (especially regarding technical writing!) very limited format. But nothing else seems popular. Why actually?
Are there any realistic alternatives?
Thanks for some hints!