Maybe I'm wrong, but with the advances in AI, SO was in for a major reduction in usage not matter how good they were about enabling the community and encouraging collaboration. I realize that your mileage my vary with modern AI, but the AI has an immediacy and interactivity that together are impossible for SO to overcome. At this point their best option might be to find a way to pivot to an AI based interface while still trying to find a way to reward and leverage the expertise of people. Even with that I suspect it's too little, too late.

I think so too, but many people have many oppositions to AI and would prefer knowledge to be in the hands of knowledgeable community, rather than AI companies. SO was poised to be this alternative, but leadership showed they did not see value in knowledge-work for its own sake.

This seems like the most likely answer to me - though we all have our grievances with SO, the culture likely didn’t contribute to its decline as much as simply AI being a better tool.

Push factors and pull factors do much more work together than either do on its own.