Many Republicans are motivated by fear--of immigrants taking jobs (as you said), of crime or terrorism, of the possibility that God will get angry if gay people are allowed to get married. Others simply don't think liberal policies will work (even as a Democrat myself, it's not possible for literally everyone in the country to have a high skilled job. Someone has to do the low skilled work; some of it can be and is being automated but that will still likely leave people out). And when it comes to actually turning out voters, that combination often works better than counting on your voters to be "inspired" by some hypothetical perfect candidate.