alt Hacker NewsThe simplest answer is that HTML wasn't designed as a presentation language, but a hypertext document language. CSS and Javascripts were add-ons after the fact. Images weren't even in the first version. Once usage of the web grew beyond the initial vision, solutions like server-side includes and server-side languages that rendered HTML were sufficient.
I think the best examples of HTML in that regard is HTML-rendered info pages[0], for Emacs and its ecosystem. Then you have the same content presented in HTML [1]. Templates were enough in the first case. Includes are better in the second case due to common assets external to the content.
[0]: https://www.gnu.org/software/emacs/manual/html_node/emacs/in...
[1]: https://emacsdocs.org/docs/emacs/The-Emacs-Editor