1. Immigrants in general have to be motivated to move. This is why Lebanese immigrants in Africa are entrepreneurs and business owners at a much higher rate than the ones in Lebanon. It is why Chinese in Malaysia were vilified and prosecuted for being rich business owners, because the ones who moved abroad were more likely to start a business.
2. Many Caribbean and African blacks have not bought into the narrative of victimhood, though the Caribbean blacks were as often slaves and the Africans readily enslaved each other. But they don't use that history as an excuse for not doing anything today.
3. Having grown up in majority black cultures, it is much harder to blame white oppression for bad schools, broken homes, crime. You can blame local culture, but not a large segment of the population. So they are more likely to value education and employment, instead of American black kids who are often attacking other black kids for "acting white" when they get As or join chess club. There aren't African immigrant children being told you can't act middle class, study hard and go on the college track because that's betraying the tribe. Hence, more success for their children.
4. When a child is born out of wedlock, even if parents live together at the time of the birth, the child is 2-3 times more likely to be held back a grade, drop out of school, commit suicide, be mentally ill, become an addict. For African Americans, the illegitimacy rate is 80%. For African immigrants, it is far lower. Family formation fights poverty by getting both parents to invest in the family AND they are more likely to save for goals like retirement or college than even cohabiting couples with children. Marriage moves you to a longer term mindset, with or without kids. African immigrants are more likely to be married when raising kids, and thus save and invest and plan ahead - and thus less poverty.