I disagree that it is a “cultural norm”. Roughly 38% of black women between the ages of 18 and 44 are single with no children (the highest of all groups). Around 30% are married. Thus, the out of wedlock births are comming from around 32% of black women and individuals within this 32% tend have have on average more children than married black women (which causes high percentage of out of wedlock births).
Around 25% of black Americans fall below the poverty line and this group makes up the majority of the 32% who have children out of wedlock. Unfortunately black culture is often defined based on the behavior of its lower class as opposed to the behavior of the other 75%.
Around 70% of black kids are born out of wedlock; that’s what I meant by calling it the norm.