The following is an excerpt from Willard Jenkins’ latest book, Ain’t But a Few of Us: Black Music Writers Tell Their Story, which was released in December. The author and sociopolitical commentator Robin D. G. Kelley is currently the Gary B. Nash Professor of American History at UCLA. Formerly a professor at USC and at Columbia University’s Center for Jazz Studies (where he held the first Louis Armstrong Chair in Jazz Studies), Kelley has written extensively about both jazz music and hip-hop. I remember a poem the late Jayne Cortez used to perform, where the line was, “They want the oil / but …