Bernie lost because the DNC screwed him over. Calling him a racist is one of the many ways that they did that.
I agree that voters prioritize other issues over labor, but the Democratics refuse to take action on those issues as well. Maybe they could try doing what the voters want for a change, and see if people come out to support them.
Then maybe we should offer the left a candidate that they'll vote for. It'd be a nice change of pace.