Causes sometimes also become popular by being popular, in the same way that the Mona Lisa is a good but not exceptional painting that became famous for being famous.
Mumia Abu-Jamal is one of countless people imprisoned in the US but became *the* cause celebre prisoner among the activist left primarily by being famous. Entirely separate from any question of the worthiness of his cause is the simple fact that calls for his release, and *only* him by name, have been omni-present at countless and entirely unrelated leftist events.
I suspect Israel is an example of this process, by which the prominence of activism against Israeli crimes reinforces its prominence in a positive feedback loop.