This is mainly due to the drug epidemics isn't it?
[1] http://www.pewresearch.org/fact-tank/2018/08/07/for-most-us-...
You'll find Jamaica, Syria, Guatemala, Pakistan, Venezuela, Iraq, Egypt, Mexico, Kenya, and a whole host of countries that are far poorer off than USA but have much lower suicide rates. You'll also notice that Japan and South Korea are higher than ours. Why is that? Poverty or economic hardship is not a predictive indicator of suicide.
Sure, millennials had to come of age during the big recession of 2008, but the economy has largely recovered...and graduates today have excellent employment opportunities.