I have a theory. It's based on my observations of bigoted hiring managers. And it goes like this.
_IF_ you don't think black people are smart/hardworking/worthy, then your department will not have any because you won't hire them.
_IF_ you become forced to have some due to corporate pressure, it will not change the fact that you think there are not any qualified, at all.
_THEN_ you will take the first black you see and not care about their qualifications because you think they are all the same anyway, so what is the point in looking for this mythical "serious" candidate? it's a waste of time and you think everyone knows it.
_THEREFORE_ the person you hire is more likely to be a poor fit because you never bothered to vet them, since you don't care and don't think vetting can identify any black candidate that is superior to any other black candidate.
And of course, when you wind up with a substandard candidate, this will validate your view that ALL black candidates are substandard, because... see?
I have observed that bigoted hiring managers tend to find the least qualified black candidates and hire them. Failing to vet and look at two or seven or fifteen black candidates to find a good or best black candidate because they truly believe there is no good black candidate and searching is a waste of resources.
Meanwhile hiring managers who sincerely believe that candidates who are black are good and bad in the same proportion as candidates who are white will look at as many candidates as needed of any race and will weed out the weak candidates and hire outstanding talent of any race or ethnicity.