Upvote:1
One reason was a gender imbalance, a lot more male slaves (captured in war), than female slaves.And of course, "breeding" requires both.
When slaves were shipped to from Africa to America, there was a reasonable balance of male and female slaves that were bought or captured, and taken across the Atlantic in ships.
Very few ancient ships carried large numbers of women.The carvels of the Middle Ages were sufficiently comfortable to accommodate women (some came over on the Mayflower, for instance).