The point is, if every one of those deaths were someone who presented a credible threat and were actually trying to kill an officer, why do so little of them succeed? If anything, they have the element of surprise on their side. Police are often only given little ammunition and training time every year, literally just a couple boxes of ammunition. Anyone just casually going to a gun range every couple of months for fun is going to have more experience than most law enforcement officers.
If they were only killing every criminal that actually attempted to kill them and had the means to, there's no chance the defenders in that situation are coming out successful 20 to 1.
Criminals using deadly force against police probably have intimidation/escape as their goal, not murder. But from the perspective of the police officer, you can't wait to find out. When a police officer starts to shoot, he has essentially made the decision to keep shooting until the threat ends.
If they were only killing every criminal that actually attempted to kill them and had the means to, there's no chance the defenders in that situation are coming out successful 20 to 1.