Privacy

They are recording what the police do and say. It clearly doesn't make a difference that the camera is technically pointing away from them. Do you think this person would have been ok with wearing a corporate bodycam because it isn't pointing at her? No obviously not.

The thing that is different is that police have control of it, and they generally only use it in public where there's no expectation of privacy, and they're the bloody police and have guns and kill people!