It was less sexism and racism than it was:
a) She wasn't likeable. This was apparent before she was VP and after she was made VP. There were whole articles devoted to it:
2024 after Joe dropped out:
https://www.sacbee.com/news/politics-government/capitol-alert/article289792134.html
2024 before Joe dropped out:
https://www.moderntreatise.com/opinion/2024/2/19/third-way-why-dont-people-like-kamala-harris
2022:
https://www.bbc.com/news/world-us-canada-60061473
2021: Even her own staff hates her
https://www.politico.com/news/2021/06/30/kamala-harris-office-dissent-497290
2021:
https://washingtonmonthly.com/2021/06/10/why-they-hate-kamala-harris/
b) She has the same sincerity problem Clinton has. Nothing about her seems genuine, the smile never quite reaches her eyes, her laugh is fake, and it all comes across as plastic and insincere.
So when she said she wasn't going to ban fracking, nobody believed her.
When she said, repeatly, she was working for an Israeli cease fire and a release of hostages, nobody believed her.
She still was a better choice than Trump.