A huge chunk of the population's lives suck. They possess a lifetime of baggage and mental health issues they've never had an opportunity to address, and lack the self-reflection even to notice. They're financially struggling, probably with massive debt, and their neighborhoods are falling apart.

Then they spend all day, every day, consuming media telling them that all their problems are caused by poor/rich people, black/white people, old/young people, or whatever.

So you have these people who are profoundly unhappy and convinced that the reason why is because of the people around them. They stomp around angrily, looking for a fight, one minor inconvenience away from losing their minds.

Source: I've worked retail.