The big reason is the purpose was to create the best Q&A site for programmers (Quora is better than most Stack Exchange sites, just not Stack Overflow) and ther

The big reason is the purpose was to create the best Q&A site for programmers (Quora is better than most Stack Exchange sites, just not Stack Overflow) and there was a relentless focus from the very beginning on making that happen. Compare to Expert's Exchange where the whole thing is designed like a liquidation sale flyer. It feels like a cheap commercialization of knowledge that is freely shared and thus feels exploitative, like it runs directly against the hacker ethos that enabled it to collect that information. Stack Overflow is very clearly designed by programmers to help programmers, and it was seeded with a great community to start it off on the right foot.