>> But take container queries, for example. They were the number one feature requested by front-end devs for a looong time. So why don’t we use them more, now that they’re finally here?

A number of things are in play here.

1) when people ask for something it's because they need it now. The client wants it to look like x. Providing it a year later doesn't mean I'll retro-fit it, I'm working for another client now.

2) the new features on offer are (mostly) not low-hanging fruit. 20 years ago we were asking for the basics - not-table layout (flex, grid), variables (var --), conditionals (@media) and so on. The low hanging fruit stuff. Now "most people" aren't really asking for anything. (The sliver of a minority attending css conferences naturally are dreaming up new edge cases.)

3) most of the websites that exist (aka have been styled) are older than these features. Since redesigns are typically multiple years apart it takes years for them to filter in. As a proportion the number of sites built, or updated, in the last year is small. And the proportion of those needing these features is smaller.

4) most sites are not styled from an empty notepad. Most use (reuse) a framework - either personal or public.

CSS is starting to move from mid-stage to late-stage development. We're well passed the "terrible to work with" stage, well passed the "good enough" stage, and now into the "what can we dream up stage".

That said I can see myself using some of these things - sub-grid and :has being the obvious ones for me.