But neither Bernie nor Warren got anywhere near enough votes in the primaries. Not enough Democrats voted for them in the end. Why do we think more independents/undecideds would have voted for Sanders?
I'd have preferred him as he's an actual leftist unlike Biden but I'm not at all convinced he would have done any better. Democratic turnout is huge; it's not like Democratic voters stayed at home en masse. Trump, against all odds, managed to even increase his own base. Not sure how you prevent that with Bernie Sanders.