@sun
a. there's a different allocation of badness in the conditions. Mass loneliness and child labor are both a single bad thing to put on a list of bad conditions, but don't have the same effect on general human happiness the same way.
b. there's a different point of comparison. Just like the coldest you might ever feel is in the middle of a desert at 100+F because your body had adapted to 130F and the temperature changed much faster than you're used to, the west remember really good times and now have mediocre times, whereas the non-west remember abysmal times and now have sub-mediocre times.
c. depression is an independent variable from bad conditions, and observing it in a society is like observing rampant endemic disease in a body: such disease is not the cause of ill health, but its growth is an opportunistic response to the immune system's collapse.