The article also goes into it, but I think the invent of AI and asking somewhat specific questions may also explain the decline. If you can get a result that can get you 90% of the way there with an AI that used stack overflow as a resource, theres no reason to actually ask on stack overflow. Its faster to go on the AI result or go on google/bing/etc...etc... that has the answer right there on the page.

And the redesign....its pretty bad in my opinion.

I was once downvoted answering a question on a library....that I created on stack overflow. Still makes me laugh.