There’s an entire machine telling them they’re right to think what they do. They have an emotional investment in it.
I think they can talk themselves into whatever they want to believe. Seriously, we’re talking about people who willfully ignore all sorts of historic geopolitical events as references for everything from populism to fascism, think their Sky Fairy has in some way ordained this anti-Christ like figure, and ignore every economic, medical, and scientific expert offering objective facts about what does and doesn’t work.
So if they’re being told there is election fraud, it exists, until it doesn’t.
It could be as simple as peer pressure and not wanting to be wrong.