Slavery systematically destroyed the family unit of slaves because it was a risk to the power structure. If there was any indication of healthy family structures forming they would split for children and men from women.
https://www.census.gov/content/dam/Census/library/working-pa...
But one wouldn't reasonably expect that to continue, no? The critics who say "slavery was a long time ago" have a point on this one. Humans getting married is very normal - if you disrupt that for a generation or two, you'd still expect it to resume. We are many generations past slavery.