I've been thinking along the same lines. It is a generalisation of course every fate is different, but I think many people growing up today in the western world seem less happy, more cynical and depressed, unable to focus etc. Basically the symptoms you describe.
I also agree it's related to having it too easy when they (we) were young. Many were born into a high standard of living and nothing was hard until they moved out of their parents home. Life was good then suddenly gets dramatically worse (Not bad, in any objective way of measuring it, but worse than they are used to.)
Compare this to their parents, who grew up from the 40s to the 80s. From the hardships of life in the 40s to the luxury of the 80s they managed to increase their quality of life little by little throughout their entire lives ending up with houses, fine cars, big salaries and stable employment. To see this progress year by year is motivating and makes people happy.
People today often struggle to reach the same standard they had when they were living at home, let alone seeing some consistent improvement. They are fighting to get "back to even", basically. You work for years in order to pay down on a house half the size of the one you grew up in, if you can even dream of affording a house at all. You save for years to go to some exotic place you already visited several times with your parents. Having a stable job in the area where you grew up and all your childhood friends still live is a fantasy, most of your co-workers are basically strangers and so on. All the things the world has to offer - you did most of them already and watched the rest in Cinemascope. The experiences are clichés before you even get there.
There are other factors as well of course, general lack of honest interaction with people, information overload, companies so large that you become anonymous, etc etc, but I think this is a big part of it. Simply put, there are many more rich people having to deal with becoming poorer today than it used to be. People are reaching goals lower than their expectations. This has always been depressing, so a certain percentage of people will be depressed by it, for a while.