This is one of the redpills. Culture is based in biology, and most blacks are biologically incapable of functioning properly in Aryan societies. I say most because the extreme end of the bell curve for intelligence likely contains some outliers who can. And by "properly" I mean truly and inherently operate with the same social norms as the average Aryan.
A lot of things that dont make sense in our society actually makes sense if you consider our society began white and most of our principles are from that. For example: prisons. Prisons always seemed cruel to me, that the punishment for petty crime could be getting locked in a cage with monkeys who want to rape you. It also makes very little sense to waste so much resources on maintaining life in intentionally poor conditions for criminals. But when we imagine a white society, suddenly prison isnt cruel and the idea of rehabilitation actually seems plausible.