As someone who has indoctrinated relatives I can see how easily the psychological affects can take hold of any individual which means there is no exception for African Americans. But, it's still wild to me that there hasn't been more of a resistance, or atheistic revolution.
I understand that a minority of African Americans adopted Islam (Malcolm X) to restore the culture that had been taken from them, and it is also my understanding that black Israelites claim Islam is their religion and/or they are the lost tribe of Israel, but regardless, Christianity has been the dominant religion among African Americans
We know that Europeans believed it was their duty to save barbaric peoples by converting them to Christianity, but this is from the European side. I want to know from the African American side.
I would assume that when enslaved African Americans were kept captive on the properties of slave owners the only reading material they had access to was the bible. Since the captors believed in Christianity, they probably spoke religiously to the enslaved often, which would be one way of African Americans internalizing Christianity.
But also, the slave owners used the enslaved to teach their youth. Likely, the bible as the preferred material, allowing African Americans to have access to these stories. Since people love literature, and given the bible was the (most likely) the only source given to African American communities a commonality and culture is formed. Even illiterate people can pass down biblical stories, though word of mouth so it becomes something to latch on to.
These incidences would exponentially increase the amount of "believers" in clusters of African American communities making it the dominate religion for them, with any resistance in the future not able to penetrate the culture because A.The profound effects of religion on the mind; B. The ongoing racism and destruction of humanistic endeavors among African American communities; C. Americans as a whole believing in Christianity.
Please, help me get my facts straight! Also, I've read a few black atheists with this very same question, and this has been puzzling to my wife (not American or black).
These older answers might interest you
Why didn't freed slaves reject Christianity? by u/uncovered-history
Why did Christianity remain so widely accepted within the African-American Community after slavery ended? by u/yodatsracist
How were Black slaves in the USA converted so successfully to Christianity? by u/chilaxinman focuses more on the experienced of enslaved people, rather than African Americans post abolition.
Considering your question, you may also find interest in this discussion of the Nation of Islam Why did the Nation of Islam reject Christianity as the religion of the colonizers, while embracing Islam as a “black” religion, when Islam was brought to Africa by Arab conquerors? written by u/USReligionScholar
edit: fixed formatting, added two new links