It's not impossible to get regular people to mark up text; WordPerfect did so very effectively for many years. But it's worth remembering that (1) that was in the 1980s, when people put up with having to learn things they didn't want to because the technology wasn't advanced enough to offer them an alternative, and (2) eventually the technology did advance, and Microsoft Word came along with its WYSIWYG interface and promptly put WordPerfect into a hole in the desert.
It's also not impossible to write a static CMS that provides a normie-friendly WYSIWYG interface, rather than having everything revolve around editing text files. That's what Movable Type (https://en.wikipedia.org/wiki/Movable_Type) was, for instance, a set of Perl scripts that provided a friendly WYSIWYG interface over content stored in a database, and then ground out static pages from that content whenever it changed. But modern SSGs are pitched to developers first and foremost, so they all revolve around stuff like Markdown and Git that are about as approachable to non-technical people as garlic is to Dracula.