generally speaking we don't have black "leaders" as the word is typically used (MLK, Malcolm X etc) for a variety of reasons:
1. no great social movement to rally around - there are some issues (economic justice/criminal justice) that motivate many, but enough black people feel sufficiently removed from those worlds that they don't feel the need to participate
2. the "older" generation never cultivated a newer generation of leaders. they instead are more interested in maintaining their positions. one of the ways they do this is by essentially strong arming white folks/corporations into supporting them personally.
3. the personal failings of the jackson/sharpton are put up for everyone to see. whereas in the past, people like MLK had their personal indiscretions essentially covered up or ignored
just a few reasons IMHO