Because most likely the instructions from the judge only allowed them to find the officer guilty only if it could be shown the officer was not afraid for his life. How is this decided? It is decided by what the officer tells them. Along with any evidence that might support that. Any? Yes any, no matter how flimsy. A glance towards a closed door. A gesture towards a back pocket. A step forward. All “could” mean a weapon was within easy reach or distance.
Now the other standard is that a reasonable person would have to believe their life was in danger. That standard does not vary because the defendant is a police officer. They are held to same split second decision making that you would be. Their training does not enter into it. Their duty to protect the public safety does not enter into it. Would holding them to a higher standard mean a higher risk for police? I doubt it. It would however make them answerable for murderous actions such as the killing of Shaver.
In another place I saw a comment from a former corrections officer who had no sympathy for Brailsford, the cop who shot Shaver. The corrections officer said he had extracted violent prisoners from their cells without serious incident because he knew how to do his job. Unlike this moron Brailsford