Biden is their best hope. In this election. They should have someone better, but they don't.
Warren is good at exploiting universally hated companies/situations, and acting like she's on the common man's side.
Wells Fargo the huge bank was signing people up for accounts they didn't authorize, and Warren spoke out against it.
Facebook steals our personal data and allows it to be stolen by others, and Warren spoke out against it.
These are slam-dunk positions to take, because nobody wants to take the other side of it. Who is going to argue that Wells Fargo behaved responsibly?
However, when it comes to more complex matters such as health care and college tuition, it gets a lot tougher. These are crazy expensive reforms, and a lot of swing voters don't support them at all.
The Free Stuff Extravaganza and the Victim Olympics don't play well with blue-collar swing voters. At all.
This is where Biden has a big advantage. He's not seen as a radical who is going to hand out a ton of free stuff, raise middle class taxes, or vilify heterosexual white people. He's just a familiar-feeling, establishment Democrat who seems like a safe alternative to Trump. Plus he's going to carry Pennsylvania by default.
His biggest strength in the primary is that black people like him, while they can't relate to Warren or Bernie. People are underestimating how much Warren is going to get crushed in the primary in states with large black populations. That's what made Bernie a no-go in 2016, even if Hillary and the DNC hadn't cheated him.