A Mystery Solved

From the autobiography of Olaudah Equiano, published in 1789:

I have often asked many of the men slaves (who used to go several miles to their wives, and late in the night, after having been wearied with a hard day's labour) why they went so far for wives, and why they did not take them of their own master's negro women, and particularly those who lived together as household slaves? Their answers have ever been — "Because when the master or mistress choose to punish the women, they make the husbands flog their own wives, and that they could not bear to do."