Thing is the electoral college is basically winner take all and most black voters live in red states that Dems have no chance of winning, and the swings states both don't have huge black populations and have issues with voter suppression. Picking a black VP just because they are black probably won't have much an effect in winning the Midwest.
Not so in 16. Hillary lost ground in the turnout and lost the vote.
Meanwhile women, esp black women women saved the party in the midterms in 18.
Doug Jones is a senator only due to black women.
If blacks were more enthusiastic about Midwest white folks, then Pete (and Amy) would have got more than 0.000001% of the black vote and possibly still been in the race.
But they didn't, and they're out.
It may not exactly have to be a poc, but it has to be someone that can connect to that community, esp if they want a successor in 2024 or 28.