It just struck me like lightning. I just realised one (surely not the only) very important reason, why Stack Overflow always winds up at least once in the top 10 search results on Google for virtually any programming-related search. The Announcer Badge. When you share a link to a Stack Overflow question or answer using the “share” button, you get a personalised link including your own user ID. If that link generates 25 clicks from distinct IPs, you’ll get an Announcer Badge as a reward for linking to Stack Overflow. This badge has been awarded more than 25k times. Note, there’s also the Booster Badge (awarded around 800 times) and Publicist Badge (awarded around 300 times).
Stack Overflow uses a lot of techniques following the Gamification principle. But this particular badge is really clever. Trick your users into creating highly relevant links from arbitrary websites towards Stack Overflow helping to add relevancy to the platform and to its various questions / answers.
Well done, Stack Overflow!