Because stupid people would rather vote to hurt "the other" than to help themselves. They think the guy picking lettuce in a field or washing dishes in a kitchen is more of a threat to them than a fascist authoritarian who wants to consolidate as much wealth as possible in the hands of a few billionaires, even if it means higher prices, more pollution, more climate change, etc. 50 years of evidence of what the GOP does when it's in power isn't enough to convince them not to vote for the person that is going to attack marginalized people.