Comment by scelerat

HTML5 is a long way from the simple hypertext document format embodied in early versions of HTML. It is that way from necessity: how the web and applications built upon it using HTML have evolved. HTML started off being very simple and very accessible. One just had to grasp the concept of a tag, and that tags had to be nested and closed (sometimes), and you could make a hypertext document to serve on the WWW. One influential cohort of users, application developers, ran hard with HTML, pushed it to its limits, and continuously revised it to be an application rendering language. Anyone who merely wanted to write a hypertext encountered a complex and growing language spec.

Markdown emerged to fulfill that "simple" hypertext document role. If you're writing READMEs and blog posts, you probably don't need more than that. And I think it's more accessible (certainly less error-prone) than HTML for most people.

If you need richer semantics, HTML5 is available. And if semantics are important to you, you're probably still using HTML5 as a rendering layer and your actual semantics are processed, stored and delivered in layers much more purpose-built for that.