Because in the US religion has largely been split along racial and ethnic lines. The Black Churches here are institutions that grew out of both the slave and free black congregations in early US history. These differed from other churches by emphasizing freedom and liberation as rewards for faith. It’s also why the Southern Baptist Convention is separate from the northern one.
It has nothing to do with Jesus. It has everything to do with modern history.
It’s a religious screed. Not a history paper.