1. He's not hard left. On the spectrum, he's not actually left, at all. But, you don't actually know about that. 2. People tend to be fans of having a better economic situation. Add that this guy gets attention, and odds are good. 3. It sounds like him losing is a "they'll see" fantasy for you.
PS: You know why Trump pulled the low information voters? Cause he stole rhetoric from Sanders, and talks a lot about the economy, and acknowledges that it's not ideal for some people. He's lying when he says he'll help, but ... low information voters are low information.
PPS. There is no hard left in America, and nobody you've heard of is pushing actual, full on socialism, at all.