I 100% think it is because of culture and has nothing to do with race. I have a friend who is black, he grew up in the Ivory Coast and moved to the US for school, he is hard working, contentious, polite, and all the other things that are associated with success. This is because he was raised to value education, to work hard, to do good for the world, the importance of family, etc.
In comparison I spent several years doing humanitarian work in the inner cities of northern Ohio. There I saw veneration of doing as little as possible, hostility towards education, glorification of violence, and a host of other things that lead to negative outcomes.
I won't pretend that some people aren't racist, but no person can tell me with a straight face that the inner city culture and everything that comes with it isn't part of the reason we have the disparity in our country.