I think the problem with the Ferguson protests is that there was no central media personality or manipulator to set the narrative or even put it in a more palatable and understandable lens. At the end of the day, it might have been because it was the wrong thing to try and start the revolution over. By the time more legitimate cases like Eric Garner came around, the general public saw these cases as just overreactions.
After all, the thing that made Selma and the Civil Rights protests so effective wasn't just the media manipulation, it was the content of what was happening. Here was a bunch of peaceful black people in suits, linking arms with whites and religious officials, because they want to do something as simple as voting, which is an American treasure, and look at how southerners react to them.
No matter how one wants to romanticize it, it's simply not the same today. The goal is not as simple as the fundamental right to vote, it's the attainment of some kind of "Mama Bear's Porridge" of police reaction that few people seem to have a single opinion on what is most appropriate.