Blacks dont like Harris because of her AG past.Blacks vote in higher numbers for candidates they like.They like Biden thats why he is leading the primary and they might like him enough to get them to the polls like Obama did in 08 and 2012 but he shouldn't take any chances of them not showing up like 2016 imo.
Every demo votes in higher numbers for candidates they like.
You're entitled to your opinion, but it's not all about the black vote. It's very likely to be Biden/Warren with the caveat that Biden supports Warren in the 2024 run.