Indeed it does come up often, but your linked blog post doesn't state a single reason why "forking HTML doesn't make sense". First, nobody is "forking" anything. Second, you assume the role of a "web developer" as a given. If I, as a web "user" (reader) want to read some text (say, about gardening), then I sure want that text to be written by an expert rather than a "web developer". If in doubt, I can live with the presentation being plain; but there's no point in reading stuff about gardening by a dilettante gardener who happens to know HTML, CSS, and JS. As a corollary, "the web" fails to deliver for the domain expert as a simple means for self-publishing; instead a self-referential man-in-the-middle snake oil industry has been build.
The greatest gardener and the worst gardener in the world can self-publish equally well on the web, unfortunately proving to others which is which is outside the area of self-publishing and they cannot do this easily. This problem is also a general one for people publishing books or anything else.
It is very very easy for self-publishers to publish plain static HTML content on the Web. A good modern solution is Github Pages, but there have always been good solutions for this.
Yes, people have gravitated to centralized platforms for various reasons, and those platforms tend to make it difficult to publish entirely handwritten raw HTML/CSS, but it's not because the alternatives ceased to exist.
