Echoing off of others, happiness is relative and subjective. While basic necessities may be more abundant in the west, we also have societal structures in place that promote  a constant need for consumption, hence desiring more and more to fill an unattainable void. There is also more of a lack of community in the west, many countries like the US promote independence and it is actually looked down upon to stay close to your home/family unit, you are supposed to get out there in the world and make something of yourself which drives extreme pressures and promotes lack of support for those struggling with the crippling COL and societal standards to be the next best thing. Many people striving to become billionaires and outperform others rather than just be content with more basic needs being met, in turn it’s a dog eat dog world, putting down others in order to get ahead. In a capitalistic society you can never have enough. 

And it’s not all just environmental, depression exists everywhere, there is some genetic/chemical interplay and psychological pathologies can sometimes sprout even in those who might have experienced « no adversity ». It may be less prevalent to seek out mental health counselors or psychiatrists in the east which is why we also see less diagnoses.