The ones that struggle had pre-existing issues : - quora pivoted from quality content to cheap clickbait - SO has overbearing moderation. Chatgpt doesn't close your question the second you've submitted it. And so on. In short, quality platforms are fine.
Because you should not ask questions on SO - you should search for an answer first - asking question there was not really what most people thought it was. It is the same at work - you should first and foremost check the documentation and read stuff on your intranet and then bother other people for help. Epitome of that was "what have you tired" that was first thing in the interface for asking questions of SO and that's first thing I ask co-workers.
Somehow people did not understand all of that or did not care. AI chatbots are only disguising search as a question. It is definitely much better from UX point of view - but with hallucinations it is worse for everyone who gets imagined responses, because there is no "hey I don't know, let's really figure this out together".