Devout Christianity is a common reason. Specifically, the kind that believes abortion is murder and is the number 1 topic that can supersede all others. If one candidate vows to outlaw it and the other vows to protect it, the conservative Christian brainwashing machine gets these out-groups to vote against all of their interests to "protect babies".

Taxes is another I hear. People actually beleive Republicans are fiscally responsible and going to help these out-groups, many of whom are lower middle class, get ahead by reducing tax. Ignore the part where reducing everyone's taxes increases everyone's gains, increasing everyone's budget, and therefore not actually increasing anyone's purchasing power because the market will adjust sales price higher.

Obviously, this works on the majority demographics too. But they're closer to the in-group than who you asked about