It basically comes down to ignorance. Most people don't have the time, inclination, and/or capacity to evaluate political platforms or the competence of individual politicians. They just decide based on heuristics or "vibes". Trump seems confident and strong. Harris doesn't seem to stand for anything much besides the status quo. They don't like that there was inflation under Biden, and Trump is the opposite of Biden. They don't necessarily like Trump's attitude, but figure they don't have to like him as long as he gets the job done. That's roughly the level of thinking that's happening, in the cases where there's much thinking at all, and people aren't just voting the way their friends, family, and neighbors all vote.
Basically this is a fundamental flaw of democracy, that you leave the most important decision in the hands of the median citizen, who has no particular aptitude for making it. Of course, other systems of government have their own flaws. Like Churchill said, democracy's the worst form of government, except for all the others. (Though I would argue that the particular structure of the American democratic system is especially flawed.)
Basically this is a fundamental flaw of democracy, that you leave the most important decision in the hands of the median citizen, who has no particular aptitude for making it. Of course, other systems of government have their own flaws. Like Churchill said, democracy's the worst form of government, except for all the others. (Though I would argue that the particular structure of the American democratic system is especially flawed.)