Why is that do you think? The race aspect?
Given Whitmer's experience, feels like she could definitely have an angle here if she wanted it, but so far everyone has been in step and Harris feels like the only potential candidate.
I'm now at the stage where I'd much rather gamble on Harris' ability to gain a few percentage points than Biden's. I think she could be better than a lot of people think, and certainly better at getting messages and enthusiasm out there than Biden.
There is already the race and gender issue, so she would already be dealing with an uphill struggle before even starting. Then add to that she is a fairly dull candidate who doesn't energize any particular constituency, even her own demographic. See the 2020 primary results for more of that.
The only reason she is in her job at the moment is because Biden made a desperate drug deal with Jim Clyburn in early 2020, where Clyburn would support Biden's languishing campaign (he was losing to Bernie at the time) in South Carolina, in exchange for various concessions on the other side. She is therefore a fabrication of convenience, and not candidate born out of popular support of democratic voters. That is not the sort of person you want to put in front of a now resurgent Trump who will be flying high in the polls because of a massive wave of public sympathy that cancels out most of his negatives for the next few months.