Part of the problem was that america didn't WANT Biden either... they GOT Biden. The Dems could have got two squirrels in a trench coat elected in 2020, and the Dems chose Biden out of desperation because they had no one else, then when he abruptly dropped out so soon before Nov, all the Dems had left was Harris... and Harris was not ready to run for president.
When Obama got elected the FIRST time, the Dems should have been preparing their next candidate... and they did nothing. The Democratic party failed the Democratic party... BIG TIME. Biden didn't help by dropping out when he did; dropping out showed the american people how disorganized the Dems were/are. Harris NEEDED at least one more term as VP, and she NEEDED to DO SOMETHING that got her noticed, Harris had nothing of substance to offer the american voters... except woman's reproductive rights, and she kinda wussed out on that in the end too. Harris's platform ended up the same as Biden's: I'm not Donald Trump. Hell even I wouldn't have voted for her.
If Biden had done anything spectacular in his term it would have shone a favourable light on Harris, but he just muddled through his term, then quit when the going got tough. Not exactly a dynamic example to follow up on.
Harris, and the Dems got out politic'ed and, sorry, rightly so.
The sun has risen and set twice since Mr. Trump got elected... maybe we'll make it
TL/DR: The Dems put up a mouse for election when they needed a lion to win