It's also very clear that their dialect comes from their poor understanding of the English language and their ability to grasp simple grammatics. They misspell their own children's names. They painfully mispronounce half of what they say. It is very apparent, when you throw down your political correctness and simply observe, that black Americans are, generally, of substantially lower intelligence than their European peers.
Evolution has it that way.
All creatures evolve and the more intelligent individuals within a group succeed in breaking away from the mainstream population. This is the beauty of evolutionary dynamics. The new groups of higher intelligent individuals clearly become the more desired groups as their survival of the fittest would have it. There needn't be any shame in admitting that we are not all created equal. If we were, evolution would not be necessary, yet we know that evolution exists in all forms of life on Earth.