You know sub-Saharan Africa isn't a monolith of poverty, poor education, malnutrition and violence, right? Anyway, the reasons some American blacks speak like that is because there is a deep seated anti-intellectual strain among a large portion of the American-born urban black population that disincentivizes education on the grounds of it being too 'conformist' to white Anglo-American culture. It's one of their worst cultural traits. Thankfully this isn't present in say, Texan Nigerian or Ghanaian culture, and they're among the most well-educated and affluent nonwhite populations in the entire country.