This might be the issue:
I’ve known four managers who won’t hire American blacks or won’t hire Americans in general.
All were foreign born.
"I’ve known four managers who won’t hire ~ Americans in general."
This is typically only an issue because they do not want to pay the wages to get quality American workers. It is not a lack of quality American Labor; it is the corporate desire to pay as little as possible as the primary driver above all else.
Seen it even in the nuclear industry which is why there is literally a class action suit against all the American Nuclear power plants for corporate wage suppression.