One answer could be that people don't really think that a superintelligence is possible. It doesn't even enter in their model of the world.
I think something else is going on. The responses to this question about the feasibility of strong AI mostly stated that it was possible, though selection bias is probably largely at play, as knowledgable people would be more likely to answer than the ignorant would be.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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