Identifying a viable villain and being mad about it would probably have helped, but the election pretty clearly shows that moving left would have had a _worse_ result.
Harris didn't run even a center-left campaign, she pushed center-right except on a few issues at the margins and it was late in the game on that front.
Americans generally favor more liberal policies economically, like stronger labor rights, universal healthcare, student debt cancellation etc. There was a lot to offer voters of all stripes there.
I think too many Democrats counted on a huge pro abortion turn out of women specifically and that translating into democratic votes, which, even to my surprise, it did not.
Harris did nothing to distance herself from being strongly associated with that liberal cohort. Regarding social policy and ideology, she came off as being far-left to the average conservative.