Seven times more? Why is that?
1) Unlike most other countries, the US is not dominated by one ethnic group. Even Canada is still more or less Anglo. We used to norm and properly assimilate immigrants. We don't any more. And we don't norm in other ways either - tolerance and diversity make it impossible to enforce any norms.
2) The US, in undermining its culture, has allowed consumerism to fill the void. Consumerism can bring out anti social and criminal behavior.
3) The criminal justice system still cycles people in and out, and lets many criminals off the hook. This breeds a culture of acceptability of crime.
4) Our prisons allow gangs, jailhouse imams and other liberal ills. This breeds crime organizations and violence. Even many European prisons are far more controlled than ours.
I could go on and on with this, I think you get the idea.