It has more to do with racism than pure stupidity IMO.
White America REALLY didn't like having a black president and we're still seeing the backlash from that. Combine that with fears about becoming the minority and the right wing media and you have a population that will knowingly vote for someone they know is bad just to screw over the people they hate.
People don't understand that to white America, Obama was all of their most hated things rolled up into one.
A black man
A university educated elite
Raised by a single mother
Son of an immigrant
Foreign name with Arabic middle name.
That shyt infuriated them and they got ptsd when they saw kamala Harris who was the same thing on top of being a literal coastal elite and a woman.
To them she represented a loss of prestige. It didn't matter what she said because to them it was all lies and her real plan would be to spend their tax money propping up immigrants(who in their mind contribute nothing to society and are quickly outnumbering whites), sexual minorities, black people, and people who live off government welfare. They thought she'd just continue to give resources to people who aren't them and continue to make life easier for the people they are competing with.
Trump centered his campaign around the dominant group(white men) the messages focused on their anxieties around race(they're eating the dogs, they're eating the cats) and their anxieties around gender(she's for they/them, he's for you).
And he tapped into nostalgia( there weren't any wars when I was president. Groceries didn't cost as much as they do now when I was president. Was your life worse or better?) And if you were a white person that was a solid appeal because life for whites was not worse when he was president.
Nevermind that the tariffs and aggression towards China that HE STARTED led to the inflation. Never mind the fact that he deregulated things so these megacorps could charge more. None of that mattered to them because of their stupidity and anxiety. All they thought was "oh fukk, not again" when they saw kamala.