Because humans decide how they are used, and all of the circumstances surrounding the camera's operation, and how they fall within the law. A wide range of things have happened that ended up in millions of citations rescinded, thousands of cameras removed, and thousands of signs changed/removed. When this happens it is ignored until it basically gets picked up by the news, and turned into a PR nightmare for them. Even then, it often takes years for correction. Even if there is a correction/payout/whatever, they rarely admit fault, and the news, always afraid of a lawsuit, never comes out and says "you know, this keeps happening, maybe this isn't just mistakes".