A weird random thought from a white guy... but... historically speaking, a lot of black folk were taken from Africa and owned by Christians, many of whom primarily only "allowed" their slaves to read so that they could indoctrinate them into Christianity. Post-slavery, a chunk of ex-slaves converted to Islam, which is ironic when you factor in that Muslims were involved in the slave trade as well.
I don't know (because, yeah, I am ignorant but at least I'm willing to admit and learn) what beliefs were held by African slaves before they were abducted into slavery... but it has been a little amazing to me how many did over the generations seem to willingly take to a religion held by their slave owners/sellers back in the day.
It would make WAY more sense to me to see a lot of modern-day atheists in black communities worldwide outside of Africa or African colonies by other nations... but I have to say, I can't honestly think of a black person I ever met that wasn't either Christian or Muslim.