Let's be honest, Stack Overflow and that network of sites has been in decline for years. Sadly it has turned into a vast and wide content farm and SEO ploy that is full of search spam and and users who copy/paste material from legitimate sources. To top it off, Stack Overflow uses "nofollow" on the outbound links to make sure the true source of material gets no credit in the eyes of Google, Bing, etc. Rinse and repeat for years, and spammers have taken over the asylum, with some trolls for good measure too, and that's unfortunately much of Stack Overflow today.
How did this happen?
In short, they appeared to receive preferential treatment from Google after complaining very publicly and loudly about not ranking at the top of search results. Ever since then they have widely dominating search results for any vaguely related technical query. Ironically, at that point in time their primary complaint was about other content farms scraping their content.
https://blog.codinghorror.com/trouble-in-the-house-of-google...
http://www.businessinsider.com/exclusive-qa-quora-may-be-tur...
>> JS: All of these sites that go to Stack Overflow, scrape our content, and reprint it with garbage ads, Google Adsense-encrusted pages.They're basically producing worse versions of our pages and they use these slimy SEO techniques, so they actually rank higher than us.
>> For a long time, we were getting enormous complaints from our own users that they'd search on Google and they'd find Stack Overflow content that had been stripped from its useful form but SEO'd like crazy and encrusted in ads and thrown up willy-nilly. And these sites were getting a lot of traffic. So that was his complaint and of course he phrased it in this larger frame of "Is Google losing their edge, etc. etc.?"
>> BI: It got a lot of attention. Do you think Google's doing a good job of fixing this sort of problem?
>> JS: They fixed it. They called us up at the time and said, "Thank you for bringing that up. You have lit a fire under the team that is supposed to be working on that problem that has not been delivering."
Matt Cutts, then the head of Google Web Spam, posted to Hacker News about this to "fix" the problem of sites outranking Stack Overflow.
https://news.ycombinator.com/item?id=2152286
What seemed like newly preferential treatment directly impacted hundreds of other sites that lost huge volumes of their traffic to the newly crowned king-of-search Stack Overflow. For example:
https://www.daniweb.com/digital-media/digital-marketing/sear...
>> As many of you know, DaniWeb was hit by a Google algorithm update back in November 2012 and we lost about 50% of our search traffic. In investigating the issue, I discovered that DaniWeb, in addition to most other programming forums out there, all lost their google traffic to StackOverflow.
That, in turn, perpetuated the reposting/scraping activity and blatant spam posts to the StackOverflow network, since the site network ranks dominantly in every vaguely related query. Now years later, an even larger volume of material on Stack Overflow is not original content and doesn't even pretend to be. It's absolutely littered with copied/pasted content and blatantly spammy/promotional posts from around the web.
From the outside looking in, it appears that Stack Overflow has become exactly what they once actively complained about.