Or perhaps it is because they have an entirely different culture? One where violence had a severe cost just two generations ago, just about the same time had all cultural celebration of violence stomped out by foreign influence, and at the same time their national defense was overseen by an entirely different country so there was no nationalistic need to push any type of propoganda for desiring a career relating to violence on its young men. Assuming you could snap your fingers and make all the guns go away in America, you still haven't solved the underlying problems of undertreatment of the mentally ill, mistreatment of the poor, and the prevailing attitude that I'm not responsible for my own actions.