Given that we're talking about a national election here, I can somewhat sympathize with those who fail to vote because the expected utility of the vote is either zero or vanishingly small. But does the same logic apply to local elections, especially those in rural areas or small precincts where individual votes suddenly carry a much stronger weight?

"With 300 million available candidates, many of whom are not nincompoops, why does America keep electing nincompoops to political office?"

The whole argument breaks down rapidly if you believe this point is false because an overwhelming majority of people are, in fact, nincompoops. Even more so if you believe anti-nincompoopish behavior is exceedingly likely to bear a high social cost (including being 'unelectable').