Kamala is not that well-liked in the black community and is seen by many as a token.
Biden’s own rep with black voters is stronger than hers, by virtue of being Obama’s VP for 8 yrs and him getting the nod!
Harris has been massively handicapped by needing to be in DC full time until November to be the deciding vote in the Senate.
Since then she's been doing a lot more vice-president-y stuff and if Dems continue to gain in 2024, I imagine they'll spend 4 years really pushing her to the front and making her more popular.