I find this curious too. A few years ago, after Mumia has received a stay of execution and the amount of activist interest in his case settled down, there were more than a few Mumia activists who suggested that perhaps more credibility could be gained for Mumia's case if the Mumia movement did more work on behalf of other prisoners on death row. Surely a movement that turns out 10,000+ for a Mumia rally could have some impact on a few selected death penalty cases.
There were some attempts to do this, but I never saw this strategy tried. It wasn't the Mumia movement which sat down and started looking at death penalty cases in Illinois. It was students who did that and their basic work created the conditions for a state moratorium on the death penalty. Their work also started generating more awareness around the country about death penalty convictions and evidence.
After my experiences with a local split several years back, I pulled my energy out of the movement and spent some time reflecting on it. Most of you have heard some of my thoughts on the movement. I think the Left groups which spend so much time on Mumia's case do it for several reasons. The main one is that it is a campaign which draws plenty of radicalized people and activists, who are potential recruits. Secondly, their work on Mumia's case lends their group with much needed "revolutionary authenticity," especially with people of color. It's hard to get down with "black panthers" if your little sect is predominantly based in White academia. Mumia is an articulate African-American revolutionary, so would be "revolutionaries" gravitate to his defense.
You can't get much "revolutionary authenticity" by working on behalf of a death row inmate who isn't political and killed some convenience store clerk.
Chuck0