Single motherhood is both a cause and a symptom of poverty, but not an absolute predictor of indigence.
Two of the “succeeding” groups you identify — Native Americans and Latinos — rival blacks in their rates of single motherhood.
Family structure & race/ethnicity shape poverty rates for children.
Note the absence of Native Americans from the above table. Their stats often go unreported because they’re just 1% of the population, and because the news is grim: of all ethnic groups, they are the poorest, least employed, shortest-lived, most likely to be crime victims, etc.
While unwed motherhood clearly contributes to poverty, this is not a uniquely black problem. African American indigence stems partly from poor choices made by the living, but is also a legacy of bad deeds done by people long dead.