I think what Bernie is saying is that for decades Dems have paid lip service to working class concerns while not actually doing much. In reality Dems have been much more beholden to corporate interests.

By the time these plans came out, too many working class folk were already disenfranchised. They saw a party that was vocal about social issues that frankly were not high on the list of priorities for most of them. They were more concerned that inflation was out of control and they could not afford basic expenses. Sure Trump was racist but at least prices were lower when he was in office, or so they would conclude. If he could bring prices down, they would go with him.

Basically Dems were just out of touch with the most important part of their base until it was too late.