Suppose your personal stake in a presidential election is $50,000 (e.g., you make $500k/year, and Candidate 1 will raise or lower your taxes by 2.5%/year.) Your odds of swinging the election with your vote are 1 in 100 million (assuming 100 million voters).
Your expected gain from voting is $0.0005. Therefore, you will not rationally be willing to spend more than $0.0005 determining which candidate is best. Further, you might deliberately vote for the wrong candidate for expressive reasons. I.e., if you assign $0.25 worth of utility to supporting the guy you want to share a beer with [1], or to proving you aren't racist, you will vote for the worse candidate.
[1] Because the stakes are so low, most people didn't even bother learning that this candidate doesn't drink. That would take more than $0.25 worth of effort.