Friend in my group was in the public beta back in '08. We all ended up signing up by the end of '09. I used it off-and-on over the years (have some questions and replies with hundreds of upvotes). Though SO had a rap for having what might seem like harsh replies or moderation, it was often imho just blunt/curt, to the point, and often objectively defensible. I also agree with your timeframe that, in the later 2010s, the site became infected with drama, and moderation suddenly started reaching its tendrils into non-technical areas, when it should not have. And on an ostensibly technical site, no less!

I found myself contributing less and less (same with Wikipedia), because I merely wanted to continue honing my craft through learning and contributing technical data with others who shared this same passion... I did not want to have politics shoved in my face, or have every post of mine have to be filtered through an increasingly extreme ideology which had nothing to do with the technical nature of the site. When I had my SO suspended with no warning or recourse for writing "master" in a reply, I knew it was time to leave for good. Most of the admins on the site transformed from technical (yet sometimes brash!) geeks, into political flag-waving and ideology-pushing avatars (including pushing their sexual agendas front and center), and not of the FSF/FLOSS kind, either.

These types of dramas have infected nearly everything online, especially since 2020. Even Linus has lost his mind with pushing politics into what should be purely technical areas https://news.ycombinator.com/item?id=41936049

LLMs were a final blow for many reasons, though I think that a huge part of it is that LLMs won't chide you and suspend/ban you for wanting to stick to strictly technical matters. I don't have to pledge allegiance to a particular ideology and pass a purity test before asking technical questions to an LLM.