The obvious culprit here are the LLMs, but I do wonder whether Github's social features, despite its flaws, have given developers fewer reasons to ask questions on SO?

Speaking from experience, every time I hit a wall with my projects, I would instinctively visit the project's repo first, and check on the issues / discussions page. More often than not, I was able to find someone with an adjacent problem and get close enough to a solution just by looking at the resolution. If it all failed, I would fall back to asking questions on the discussion forum first before even considering to visit SO.