Often the people curating the questions are also the ones who are answering them.
Their goal (loosely described) was so that if you pulled up the front page of the site, you'd find questions that are interesting to read and answer.
If you, as a professional visiting the site went to it and found the front page with things that were trivially answered by reading the documentation or "how do I draw a triangle with stars?" ( https://stackoverflow.com/q/10932962/ type things) you, as a professional, are less likely to stick around.
In the period, Stack Overflow was reducing the ability for people to curate content and trying to boost "welcoming". https://stackoverflow.blog/2018/04/26/stack-overflow-isnt-ve...
Part of this is that much of the early writing style was intended to mirror technical writing. In reading https://learn.microsoft.com/en-us/powershell/scripting/devel... one doesn't find "Hope that helps" at the end of the page.
It takes a while for a person to understand the norms of writing for a given audience. In the early days, people either came to it with that mindset or were able to be given more attention and guidance as to what the expectations for the site were. When Stack Overflow become extremely popular with college students and people outsourcing their work ( https://news.ycombinator.com/item?id=48960245 ) the ability for the... for lack of a better term "elders" of the site to try to get people to understand how the site worked and its expectations.
Many of the new users expected Stack Overflow to work much like forums - with a back and forth between people and a chat like environment... that wasn't so. The use of the curation tools to try to help onboard a person were deemed as unfriendly and "toxic" started getting tossed around.
Stack Overflow corporate, trying to be sensitive to the broader cultural movements at the time and the "we need to make this a more inclusive space" made it harder to curate and began a campaign of removing or limiting curation tools as part of "welcoming".
During this time, there was one tool that was enhanced in its effectiveness. If you had a gold badge on a tag you could close it as a dup of another question categorically. Rather than "this question is poorly written and it is unclear what you are asking" (requiring 5 close votes from different people - that would never happen if it didn't happen in the first few minutes because few went to the review queues) they could close the question as a duplicate of what it might be.
That didn't help things when it came to the perception of the site. It was a last ditch effort to try to make it so that the front page was the well asked questions.
Combining the reduction of curation tools, labeling their use as gatekeeping, the growing ratio of new users to elders, and corporate quite literally saying that those people who were doing the curation were the bad guys... well, a lot of them left or reduced their activity.
That in turn made it so that it was harder to find the well asked questions and fewer people were around to answer questions. Note I write "well asked" not "valid" - a lot of people claim to have a valid question but don't ask it in a way that is well suited to the Q&A format.
Combine that again with reductions in staff, various awful "experiments" in the name of improving engagement. That was akin to firing half of a construction team at a house while having them add a new patio... all the while the basement is flooded.
And so you've got what is there today. Very few curators left compared to 2016. Few caring answer new difficult questions. The easy college homework questions (how do you draw a triangle) and the outsourcing of work to free labor is now done with an LLM... and there's no coming back from that. ... And few people believe in the mission goal of Stack Overflow - and those who do, don't believe Stack Overflow corporate believes in that mission goal.