That’s because white people only come together in order to not cannibalize themselves. They don’t genuinely like each other. Uniting under the guise of white supremacy is a tool that distracts them long enough to stop fighting themselves and exert their lust for violence on other people.
Remember this whole Palestine-Israel conflict is a direct result of them globally waring with each other despite basically conquering the world. Despite total world domination they still found a way to fight each other across multiple continents.
We don’t have that problem as melanated people so it’s much harder to unite as one ethnic group. We don’t naturally hate one another nor does our culture revolve around violence and war.
Another reason is because all Caucasian countries are pretty much all the same culturally so it’s far easier for them to form one monolithic culture of white supremacy. We are far too diverse culturally and would be doing ourselves a disservice in doing so.
Anglo-Saxons are legendarily ruthless in getting everyone to tow the line--colonized the Irish, jacked Greek culture and civilization while excluding them from "Whiteness"
And it has worked for them, and even more spectacularly well since 1945. They've basically shaped the world with that as their core doctrine and this is how they've had British Empire----> US Empire-----> ?
Black people tend to be a bit more welcoming of Foreigners than our own kind. Tribalism is our Achilles heel and its why slavery, colonization, Apartheid was so "easy" to execute. We have tribes that hate each other so much, they'd rather everybody suffer under European rule than see another tribe reign over them.