Intact black families are a narrow slice of that population, whereas intact white families are a watered-down majority of theirs.
However if you go back in time you discover that it was happening before the 1960s when you were more likely to have intact black families. Intact black families were as or more likely to advance financially.
When the Great Society came along all the progress that had been made not only with black families but all people that were poor was reversed. Out of wedlock births, violence and STD which had been dropping suddenly started going up.
I know, even here on FR, it is not considered trendy to point out that getting married is a overall social, financial and emotional advantage but it is.