Police officers in America shoot too often. In 2018, American police officers fatally shot 1,000 people comparted to 11 people in Germany. That is absurd, considering that the US population is only four times as large as Germany's.
Above all, training is insufficient. Compared with other developed nations, police training in the US takes a ridiculously short time. Police recruits in other countries learn how to solve disputes with the least amount of violence. I do not know the specifics of American police recruitment, but if the US is not nearly 100-times more dangerous than Germany, then American police officers tend to be more trigger-happy. Which is horrible.
To be fair, I guess part of it is the fact that the US has a ton more guns. When everyone can have a gun, it is much riskier to arrest someone and I can see why American policemen are more trigger happy.
Of course that probably does not explain the entire gap or even a majority of it, but it is still a factor.