One possibility is, blacks may be looking at the Sanders promises and asking, “What’s in it for us?”
Case in point: free tuition for public universities - er, that assumes that you are accepted into the university in the first place. (Sanders keeps going on about how university education is a right, but doesn’t address what to do when the number of potential students exceeds the school’s capacity.) It’s also possible that leaving private schools out may be considered an attack on Historically Black schools.