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.

Having experienced the SO culture, I like to think the culture caused it - schadenfreude - but it was probably inevitable given AI.

Even if SO was the most wonderful friendly place in the galaxy, would you rather post a question and wait hours for a response, or get one instantly?

And in some ways AI "search" works like SO - you ask a question, you get an answer. If you don't understand the answer or something in the answer you ask for clarification and it provides it. And you don't have to wait a day or a week for it. (Ofcourse, the AI gets it answers from human curated info pools like SEs, pirated books etc ... but if these sources shrink / die to AI, it may not be able to provide new and current information, and we'll be back to SEs and Reddits and HNs again).