That's where the "police are heroes" bs comes into play. A regular person who claims to have feared for their life objectively unreasonably will get laughed out of court and straight to prison, but when a cop does it people think "well they do have a dangerous job..."

Jurors have to swear an oath to follow the law as it's explained to them by the judge, and the laws are made to protect cops. It's as simple as that unfortunately