Back in the 1950s, in one of the earliest works of rational choice political science, Anthony Downs posited the irrationality of voting. In essence, the chance of your voting being the deciding one is so vanishingly small that it didn't make any sense to vote, even if you perceived a large difference between the candidates. Since then, rational choice theorists have had a hard time explaining, within the bounds of rational choice theory, why so many people do vote. (Some have, however, put theory into practice. Downs once told me that Gordon Tullock, another important rational choicer, came up to him at a conference and said, "Tony, after reading your book, I stopped voting.") This Washington Post article might just provide a partial answer for them:
As swing states with large elderly populations such as Florida gear up for another presidential election, a sleeper issue has been gaining attention on medical, legal and political radar screens: Many people with advanced dementia appear to be voting in elections -- including through absentee ballot. Although there are no national statistics, two studies in Pennsylvania and Rhode Island found that patients at dementia clinics turned out in higher numbers than the general population.
There it is, voters act irrationally because they are irrational! QED