The Harris selection quickly sliced the Dem voter base, as she doesn't have much appeal to voters generally. The Bernie-progressive side is furious, and even run of the mill normie Dems don't care for her. She dropped out in December before voting even began because she was polling so low and ran out of "funding".
The Dem voting coalition is not unified or excited behind this President/VP ticket. Even hardcore Dems like Cenk came out and said even if Biden/Harris won they would work to primary them out in 2024.
Meanwhile Trump, despite his failings on a policy level, has averaged around ~95% approval from Republican voters and set records for primary voter numbers even though he was unchallenged as the incumbent president.
She dropped out because Tusli exposed her for the criminal that she is. I wonder how many innocent people and non violent offenders she has sent to jail.