Finland has guns, but little gun crime. I suspect Finland has neither a melting pot of people that the US has and that it has a much better public health system for the poor and disadvantaged than the US does.
Well, not sure how the "melting pot" plays into this, many - most! - shooters are born & bred in USA. And it doesn't seem many are particularly poor and disadvantaged, at least in the sense that the homeless and / or truly destitute are the ones carrying out mass murders.
The United States doesn't lock up its crazy people and doesn't provide a reasonable option for their mental health treatment.
All western countries have been de-institutionalizing their mental health patients to varying degrees of disastrous consequences.
They don't have monthly mass shootings either.