When you're farting around, you want to read “fun” questions and answers (e.g. “Interesting uses of sun.misc.Unsafe”), and when you see stackoverflow moving away from the “fun”, you have time to write an angsty blog post (because you're just farting around).
When you're trying to get work done, you want to find direct answers to specific questions (e.g. “how do I do X in JQuery again?”). The Powers That Be want stackoverflow to focus on this kind of Q&A, so you're not likely to find your question closed for being off topic, and even if it is, you don't have as much time to write an angsty blog post (because you're hard at work).
Then there's the fact that people are more likely in general to publicly complain than to publicly praise, and complaints are more fun to read than paeans.
So if your impression of stackoverflow's “decline” is based on recent posts you've seen on HN, you should try to get a more objective assessment. I don't see stackoverflow as declining based on their traffic measurements:
I think their strategy alienates people as users(like myself) from posting, but encourages consumption. I only post there when I have a difficult problem I haven't been able to solve. I think that is the system working.
They have alienated some power users, I remember a thread ~1 year ago about someone deleting their account on SO because of these policies but I suspect a lot of the pure engineers and egotists like posting and dealing strictly with interesting thought provoking content.
tl;dr What SO sees as its major asset, others may see as "decline"