Why would someone vote against their self interest? Probably for a few reasons which are justifiable in the minds of those do it, and for one reason I learned when fortune took me to visit South Africa in February 1992, shortly before the last all-White election/referendum was held in March. I ended up in a public hospital for 13 days with a salmonella infection, and got to talk with some of the Black staff while there and asked them their opinion of the upcoming referendum to continue the reforms to abolish Aparteid which would eventually lead to a majority Black government.
I was befuddled by many Black people who were against abolishing Aparteid because I did not know the Blacks were not a united group. Remarkably, Blacks trusted whites to be consistent and mostly fair in an unfair system, even though the Blacks didn’t like the system. BUT. . . ! They trusted the whites far more than the a rival tribal group “I don’t like the Whites, but I trust them. I’m Xhosa, and I neither like nor trust the Zulu, and I don’t mind if I don’t have a vote as long as the Zulu also don’t have it.”
I have a feeling Americans who vote against their self interest do so for a similar reason, namely a fear of what might happen to them if a minority group got political power over them.
Fear politics. ‘Socialism/communism’ will kill us all! /s
Also single-issues voting.
Not by accident, either.
If you are so comfortable in your life that you expect nothing to change much for you either way, voting out of spite is a possibility for you.
Many US minorities, especially most Blacks and Latinos, would not vote Democrat if it was just Ideology, but because the Dems are so unambiguously better for them policy-wise, they swallow their conservatism and vote Blue.
That is because there are always serious negative consequences for them if Republicans take over.
Voting against your interest is a luxury problem.