The users being generally unhelpful wasn't an issue for them, since they were still significantly more helpful than users anywhere else on the internet. Reddit was and still is filled with completely unvetted answers (on pretty much all topics not just programming), Quora was/is a joke, Yahoo answers had some funny posts I guess but nothing you could actually learn from, what else really was there? Before AI, Stack Overflow was as good as it gets.
It's both. Users tolerated the hostile environment to an extent as long as the site was still the best way to get useful information. When LLMs came out, that was no longer the case.
There was also the pattern of "closing as already answered" with an answer from 6 years earlier which wasn't actually answering the question when you dig into it. Certainly in the code stacks.