Well, technically, it sells "clicks" on a computer site, but it's the same idea.
If you judge your life by what you covet in others, you will always be miserable. It's always about how one exercises one's choices and moral agency.
The driving reason for this disparity is the millennial penchant for delaying traditional adult milestones. As a group, they are prone to choose short-term happiness and independence over long-term wealth accumulation. Now, maybe millennials are leading more fulfilling lives than their parents and grandparents, and maybe not. Comparing themselves economically to generations that embraced a different set of priorities at the same age, and then wondering why the results are different, however, is disingenuous.