[Cyberbob]

Bernie has many radical ideas that would be beneficial for the US, but would never actually be implemented with the current political system they have. He'd be hamstrung every step of the way.
He's gone full Populares and it's incredible to hear, but it deviates too far from what the Democratic Party will be comfortable with. See also: 2016.

What's changed in the last four years in the Democratic Party that would have me think that they've learned from losing to Trump? Nada.

Biden's well known, has the safe middle aged white guy factor, and if he stays in the race, he'll get the Superdelegate endorsements because he's the epitome of what they stand for, and that'll be that.

Warren's intentionally playing it safe, probably out of fear of alienating the potential endorsers, but isn't making headlines of any sort just yet.