To me, that's like saying, why bother having seat belts if you can still die in a car crash?

Cameras didn't help get an indictment in this case, but it may help in the future. Also, some of these citizen camera videos don't get the entire interaction between cops and victims. There might be things that happened before the camera was turned on that could make a difference in bringing cops to justice. A body camera might be more likely to capture stuff leading up to the inciting incident. I'd rather cops wear body cameras than not.