Comment by bdw5204

Nobody expected entire applications to be built out of HTML, CSS and JavaScript when those languages were being designed.

CSS's main purpose was to get inappropriate bloat out of HTML because HTML was supposed to describe content not what it looks like but the IE vs Netscape browser wars had created a proliferation of new HTML tags that went against the purpose of the language. JavaScript was designed for writing simple scripts to enhance web sites not to be a full programming language.

Web application development was supposed to be done through plugins like Java (applets), Flash and Shockwave. It wasn't until 10-15 years ago that the idea to just do all of this in HTML, CSS and JavaScript occured to anybody because it would have been really slow and inefficient on older hardware (HTML5 video on Youtube instead of Flash used to slow my mid-00s mid range Windows XP laptop to a crawl).

For CSS in particular, the expectation of its creators was that users would specify their own style sheet which would override the web site's style sheet. To the best of my knowledge, this feature ended up being little used and is not even possible in modern browsers.

(The above is what I remember from teaching myself web 1.0 style web development from books in the early 00s as a preteen and then teenager)