what's going on with black comic book characters?

why are they doing things like making the flash black? why have sam take over as captain America. what's would have been wrong with giving sam his own series? when they have this big cross over event, the black characters are almost never used. I loved the mighty avengers under luke cage. a lot of those characters have great story lines and back stories. it sold around 100,000 copies. why not do more with them? they have blue marvel. they could definitely use him more. now I see what a lot of people were crying about. both marvel and d.c. have a lot of black characters. however, they never use them. now they are doing this needless overhaul. I love the fact that comics are trying to diversify. however, instead of making legacy characters black...they can use the ones they already have. characters like static and blue marvel should be used a lot more.