Beacuse the Mumia case is very low, if at all, on their priority list, I suppose. I live in Baltimore City, and most of my working class neighbors (mostly black) have other issues on their agenda, employment, economic development, keeping their community from crime or unwanted development, etc. and they have little in common with sect and campus crackpots populating the Mumia movement. I once tried to explain the Mumia case to my black neighbors who have never heard of it, they just shrugged and commented "well, if he killed a cop, he deserves it."
I absolutely understand them. Baltimore is one of the most lawless cities in the US. Just the last weekend we had a shooting on our parking lot, someone got killed or injured. People are really sick and tired of guns and violence. They want it to stop, and do not care much about finer points of legal procedures.
wojtek