Pete had no special appeal outside of being the only moderate candidate in the race without a major liability/flaw.
Biden & Klobuchar both lose their shit on stage in different ways.
Biden has a habit of trailing off on unrelated tangents where he begins to spout off a bunch of what could accurately be described as, ironically, malarkey. And you really don't know that he's NOT going to use a noun like chinaman or an adjective like cotton picking.
When Klobuchar is forced to answer a question too far outside of her comfort zone of retelling the hilarious twitter zing she hit Trump with, she stammers, shakes, and desperately relies on friendly crowds so she can get back to her folksy talking points.
They're both campaigning as if our problems are the same ones we faced a decade ago, except with the addition of Trump in the white house. Why will the results of the 2020 election be any different than 2016?
Ultimately their candidacies represent a plastering over of problems that still loom large in Trump country, and don't address other more real problems either such as continued growth of deficit spending, continued growth of the military industrial complex, etc. Mayor Pete at least had the background and vocabulary to suggest he could approach these issues from the perspective of a compassionate, young, competent, Midwestern military vet as opposed to a dusty insider going through the same tired motions of running a primary campaign.
Bloomberg doesn't have a chance for obvious reasons.
Warren might theoretically be a good compromise candidate but she's too extreme for the moderates and too moderate for the extremes.
No matter what the DNC throws at Bernie this time he will win and then Trump will get reelected because Bernie is too associated with that other kind of socialism that Americans really really don't like.