Because their culture is severely messed up. You may also want to look at the comparative differences when you seperate Caribean blacks from American blacks.
Why has black student achievement lagged that of whites at the same rate for nearly 30 years - ever since the government has measured it - despite $billions of government money?
Because American black culture has picked up anti-intellectualism as part of it? Because those liberal programs that cost billions did nothing to address the underlying cultural problem? You are away that students in Harlem were able to rank second in the city before all those billions of dollars started helping them, right?
You need to travel to Haiti and Jamaica and observe.