It's due to the fact that such groups by the nature of their lower status can't get through with their message. Nobody cared much for slavery in the US until Uncle Tom's Cabin came out back then among other gruesome real life accounts. The average plight of downtrodden peoples just gets overlooked. Compare the global hunger crisis to the swine flu scare. Nobody cares for all the food riots and tens of thousands dying of hunger daily etc. but people go crazy about a few flu deaths.
So basically you need something shocking to get attention, whether it's a statistic, story or whatever.