That is moving the goalposts, with DHTML or not, it can be a single HTML page.
In fact I was very specific about what concepts were not possible twenty years ago: "What's being shown off here is not having a single page of a website in just HTML/CSS, but having all pages."
You're the one who proceeded to ignore that and make an unrelated claim about something different that was possible twenty years ago.
They're artificial limitations exercised in pursuit of demonstrating that, with new CSS tools, something surprising can be done. Something which, as I stated in my original comment, could not be done twenty years ago: putting multiple pages in the same HTML file without Javascript.