What I can offer as an over-encompassing yet simplistic and generalizing explanation is this: the younger generations (millennials and genX'ers, like myself) suffer from the vacuum created by the absence of a higher purpose, or socially recognized common ground. this is due to neo-liberal capitalism being the dominant ideology which seeks to individualize yet does the opposite. also intended and unintended subversion of existing social cohesion is done by our elites. I'm not for a return to the modernist "ism's".. but we should consider the consequences of our world-views.
RE: "Nordic countries' 'happy' reputation masks sadness of young" - Why and how to remedy