Kamala Harris is the whitest black woman they could find. They also needed to reassure those scared white suburban voters that, no, they really don't mean "abolish the police" when they say "abolish the police". There's no way they were going to scare off the white vote with the possibility of an actual angry black woman taking the reins. The BLM movement has made even liberal white people skittish. So much so that they've pretty much made a bunch of lefties go out and buy guns for the first time. Twitter lefties are one thing. The average lefty isn't so gung ho about reparations or giving up their own cushy jobs so they can up the diversity % in the company.
Plus, she's married to a white Jewish guy which will reassure the Jewish voters that those pesky Black Israelites aren't going to be gaining any traction.
I still say that Trump will eke out a win. And honestly, that might be what they are hoping for. You can't start a revolution if your team wins the Presidency. But you certainly can start one if he does. Or, if it is close and he demands a recount before conceding and you can spin it as him not giving up power.
I think Americans are screwed either way. I still don't know why so many people have faith in Trump. He's just as bad as all the others. He's really just another Bush who serves as the bumbling idiot that everyone can laugh at while behind the scenes the real power brokers call the shots. Biden is worse (because he's completely senile), but both are really, really shitty.