The idea of CSS Zen Garden, that was: to show that you can produce server side simple and semantic HTML, and CSS will be enough to do the rest for the presentation of the content, was an incredible innovation of 200x that was totally forgotten, and that now, younger generation of programmers that grown up with big web frameworks no longer "get". They see CSS as something complex and impossible to handle, exactly because of what modern HTML is (because of such frameworks), without realizing that this is indeed the same problem: that modern web sucks, not that CSS sucks.
What changed was that “web 2.0” happened. Web design’s focus changed from documents to applications.
CSS Zen Garden was about styling “web 1.0” HTML documents.
But dynamic UIs have completely different styling needs. People started building JavaScript applications, and they started needing UI layouts similar to those provided by desktop UI frameworks. And CSS was never designed for that. Concepts like “float” were entirely derived from the word processor universe. CSS had to add several complex new layout engines over the following decades.
