ChatGPT was released in Nov 2022, and frankly wasn't very good originally. The SO decline started occurring almost two years ahead of that, and was already on a sharp decline before ChatGPT shipped, and certainly before ChatGPT actually became good.

This is revisionist history. People told SO that they were leaving for YEARS because of how incredibly toxic it had become. It was already giving outdated answers before ChatGPT shipped, because new questions/potentially updated answers were [Closed] [Dupe] immediately.

Their answer was essentially "We aren't a Q&A site, we're trying to be a knowledge base! So closing all questions on a Q&A-stylized site, and extremely abrasive moderation, is working as intended."

They entirely did this to themselves. The community was toxic, their policies were toxic, and they didn't listen when warned as such repeatedly - just doubled down.