Well, in spite of those African slaves who still tried to retain some vestiges of their indigenous spiritualities, I would say those who did embrace Christianity were ASSIMILATING (acculturation) into a new society.
Those same African slaves had a long history of ASSIMILATING into whatever society which had CONQUERED them and ENSLAVED them before, going back thousands of years even to ancient Kemet and Nubia (Kush).
Now, no, Kemetic and Nubian slavery was not the expansive brutality of the Atlantic Slave Trade; but abuses and "disciplines" as beatings and such towards their conquered/enslaved villages/kingdoms did occur. As they warred against each other, they killed men and children and plundered and raped their women, taking them as "wives" and "adopting" the children born of the rapes.
In American slavery, the children born of the rapes of African women followed "the condition of the slave mother."
But in Kemetic and Nubian slavery, the children born of the Kemetic and Nubian rapes did not always follow the condition of a "slave" but were given and treated to all the advantages of the ruling family: education and social advances, etc..
Some historians say that in Kemet, for a time, the conquered Nubians (Ku****es) were allowed to keep their religious beliefs. The Kemetian rulers even mixed/incorporated some of their gods with Nubians (Ku****e) gods.
But, over time, this changed and throughout history, every conquering society which enslaved another group of people also controlled their RELIGIOUS beliefs.
Whatever God or Goddesses the conquering society believed in was also taught to and projected onto their slaves, even in ancient Kemet,
...in other words, "YOUR world as you knew it is no more. You are HERE now and must adhere to the God that WE, your NEW MASTERS, believe in."
Moreover, being enslaved and divided into CASTE SYSTEMS was not new and alien conditions for the Africans of the Atlantic Slave Trade.
So, here was this White man telling them that they were BENEATH him and "deserving" of their enslaved and abused conditions even according to the holy text of the God they
professed to believe in, a distortion of the Bible to fit their agendas....and, in time, the Bible also became a source of comfort to slaves, holding onto the faith that, one day, God would make
"Pharaoh, let my People go."
Even today, in Africa, some Caste Systems still exist in some ATR beliefs.
...Even today, a mindset and system of one group's SUPERIORITY over others is still evident in some ATR beliefs with certain accompanying RESTRICTIONS on social life, marriages and economic control between the UPPER caste and the LOWER caste.
The novel,
THINGS FALL APART, by Chinua Achebe, is one source from an indigenous African. This novel mentions the LOWER "Osu" in the Yoruba caste system and that religion's tradition of killing twin babies (cast away into the "Evil Forest to DIE).
Now, yes, present-day's so-called "definition" of and treatment of "Osu" in Africa is a distorted result of Christianity's introduction into Yorubaland and the slave trade....that this so-called "definition" was NOT the ORIGINAL
venerated application of "Osu" in their religion but that Christianity and the slave trade helped "create" today's view of "Osu" as so-called
tainted "Un-Touchables."
...So, present-day's "Osu" treatment is a result of what's called
"Igbo Christianity."
But, again, there's that "ASSIMILATION" again.
However, one character in
THINGS FALL APART, a Yoruba woman, had had 4 twins pregnancies and she eventually embraced the Christian church because they would not KILL her babies as the religion of the Yoruba dictated.
So, conversely, as Christianity was introduced into Yorubaland, it spoke AGAINST this IGBO religious tradition of killing twin babies; and, as a result, today, many Igbos do NOT practice this tradition any more.
...again, ASSIMILATION.
So, IMO, there are various emotional, psychological and historical reasons why a people would worship the God of the people who had invaded them/conquered them/killed their men/raped their women and enslaved them.
This ASSIMILATING behavior was not new to the Africans of the Atlantic Slave Trade. They had been ASSIMILATING into various aspects of another's culture and religion throughout every invasion since ancient Kemet and Nubia (Kush).