Because they are the first American generation significantly economically worse off than their parents.
Even US life expectancy is dropping, as are average IQ’s.
Even US life expectancy is dropping, as are average IQ’s.
0: https://qz.com/1169672/us-millennials-were-almost-20-more-li...
The depth of the depression the US per capita GDP only dropped to ~1920 levels. (Industrialization is a hell of a drug.) It recovered by the end of the depression and the 40's was a massive boom.
You really want a logarithmic scale to do these kind of comparisons over time. But even that misses the kind of structural changes that are really harming Millennials specifically.