I think it's complex and hard to breakdown. Modern life may have something to do with it, but it certainly isn't more difficult to live today than it was during the great economic depression. Additionally, the internet should tell us that If you live in the US you are way better off than people in places like Ukraine, Mexico, Argentina, Uganda, etc. Now, if they are comparing themselves to the Kardashians or erroneously to pretend-rich Social media personalities, that's on them.
I think how easy life is has little to do with psychological wellbeing. If life is very hard but you are doing great relative to others you will feel good. Furthermore, a more demanding life often generates a deeper sense of purpose and meaning.
It has to be something else. Lots of people around the world live in dire conditions, in sub-modern conditions, picking garbage dumps bathing in ditch water. And they and their friends are equally poor and living under cramped tin roof dwellings. They're not doing "great" from an economic standpoint, but may be doing well from a social standpoint and mental health standpoint. They may not be individually tougher, but as a social group, they seem tougher.
