I think people raised under conservatism, like people raised under capitalism in general, have a counterintuitive and antisocial instinct to “punch down”.

Capitalism teaches us wealth and power come from hard work and merit, if people are poor it’s because they don’t work hard and have no merit, and that poor people are fundamentally bad people.

So if they have to choose between blaming poor migrants who are willing to work for low wages - or are forced to work for low wages, because the law doesn’t allow them to work legally or access the legal protections of citizen workers - or blaming rich, powerful business owners who decide to exploit these poor migrants, that instinct overrides logic.