That is IMO a side-effect of the (from an European POV) absolutely mind-boggling, ridiculous sentencing of criminals in the US. Here in Germany, when a drug smuggler gets caught, they can expect four, five years behind bars. Not worth to shoot the cop that just stopped your car full with meth and make a life sentence out of it for murder.
In the US however? Decades, sometimes centuries behind bars. Given that perspective, it does make sense for a criminal to shoot that traffic cop - the chance to get away and escape a death in prison is non-zero.
Add to that the fact that there are more guns than people in the US, plus extremely lax carrying laws, and "stand your ground" laws.
The result are (rightfully, I have to admit) afraid and thus extremely trigger-happy cops.
If the US wants to get rid of trigger-happy cops they have to get the gun problem and sentencing under control first.