BLM picked no one. The people who run the media made him a martyr specifically because he was a vile sort. "All who must obey, listen! Give praise and copious tears to this career criminal thug who overdosed on a ghetto speedball while resisting arrest to avoid the trivial charges and momentary detention that he would have gotten for passing bad twenties, likely to clear a debt with his dealer." That's the conspiracy theory anyway. A real martyr doesn't have the same effect because everyone can agree it was a bummer.