Because a lot of people who vote Republican don’t have a real grasp on what they are actually voting for. They just know that “their people” are Republicans. My evangelical parents are the perfect example. They couldn’t tell you anything about the Republican platform other than “they want to lower taxes” (which in itself isn’t true for their income bracket). But they do know that they have always voted Republican along with everyone in their church, so the Republicans are “their” side. This is why they have a general belief that Republican policies won’t hurt them even if they don’t know what those policies are. They think they are part of one big team.