It's not that NPR doesn't like black music. It merely maintains a strict preference for black music that few actual living African-Americans listen to.
NPR's taste in these matters may be best represented by something called the DORF Matrix. DORF is an acronym for Dead Old Retro Foreign. With a few rule-proving exceptions, the black music heard on NPR falls into one or more DORF Matrix categories:
Dead: artists who have shuffled off this mortal coil. There was a significant spike in this category this summer with the passing of Michael Jackson. In general, though, NPR prefers its dead black musicians decades dead. Bonus points are awarded to performers present at the 1963 March on Washington, and to Bobby Short.
Old: musicians of advanced years. Crusty soul-belters on the comeback trail, gray-bearded jazzers, Motown legends, defunct rap groups.
Retro: musicians, young or old, performing in styles two or more decades out of fashion. Sixties soul revivalists; old school rappers who "[stick] with the puns, jokes and silly one-upsmanship that once defined hip-hop ...Thank goodness"; Lenny Kravitz.
Foreign: black folks who live in far-flung places. And/or the children of Bob Marley.
It's funny because it's true, right? Now if you'll excuse me, I'm going to listen to Keb' Mo'.