Everyone from Sanders to Dick fucking Cheney endorsed Harris. Anyone who was paying any attention and wasn't a literal fascist voted for her. The direction of the swing seems irrelevant.
The swing fell short because it's not so much about direction than strength. Macron in 2017 ran the most "hard center" presidential campaign imaginable. Difference is it worked, not because his centrist program was particularly novel but in large part because he is a very charismatic figure and managed to create a voting base of hopefuls for himself. The same can broadly be argued about Obama (whose first act as president was to essentially absolve the previous administration and Wall St of their many sins in case anyone forgot how moderate he was).
Harris ran on a platform of... "I'm not him". Which to any reasonable person is an obvious "yeah OK", but unfortunately most Americans are apathetic cretins who will refuse to move their asses to a polling station if the guy on the telly doesn't promise them a blowie at the voting booth. And the Democrat establishment is simultaneously too big to fail and incapable of producing an actually charismatic leader.
Well, all that and the obvious election interference from Musk, Putin, and the ontological inability of traditional media not to platform literal fascists.