Kamala wasn’t a good candidate for lots of reasons, including her heavy lean on identity politics, but also her history as a prosecutor, amongst other things. Booker refused to take up the mantle of moderation and thus languished as a person without a message. Klobuchar didn’t connect, Buttigieg was too young, Beto said lots of stupid shit and didn’t seem to know what was going on. Biden’s built-in support meant people like Bullock and Bennet never had a chance.
More simply: too many people thought Democrats = Left Twitter / Brooklyn / Hollywood / NE college campuses. But really, Dems just want to beat Trump; and a smaller but substantial portion, want a “political revolution” that is still not cultural far-Left.