When I occasionally venture I to standards-land, I always ask "what user research have you done on this?"
So many weird design choices in computing are because one person said "this seems right to me" without considering other viewpoints or consulting with the wider community.
Sure, you probably dont want death by committee, but a tiny cabal engaging in groupthink often produces unhelpful results.
This is true, but my feeling is that with CSS, a lot of the weird decisions are for backwards compatibility with way back when HTML was just tag soup and browser implementations were haphazard.
This feels like the origin of a lot of these mistakes (and more besides): they weren't based on "what is it that lots of real designers are actually trying to accomplish?". Why did it take so long to get support for pinstriping, when prior to that there were 1001 different ways to try and accomplish it, because so many people wanted it? Why did it take so long to get layout functionality that even just matched the power of what CSS was intending to replace? Or vertical alignment, or drop shadows, etc, etc, etc. I like CSS and the intentions of it, but man, it was designed from a place of having no idea what people wanted to do.
Many of these mistakes weren't even made by any committee, but were stuff shipped in a rush by Netscape or Microsoft to win the browser wars.
There was some (academic) reaserch behind early CSS concept, but the original vision for it didn't pan out ("cascading" was meant to blend style preferences of users, browsers and page authors, but all we got is selector specificity footguns).
Netscape was planning to release their own imperative styling language, and ended up shipping a buggy CSS hackjob instead.
Once IE was dominant, Microsoft didn't think they have to listen to anybody, so for a while W3C was writing CSS specs that nobody implemented. It's hard to do user research when nothing works and 90% of CSS devs' work is fighting browser bugs.