[BeetleB]

Frankly, you don't even need to compare richer vs poorer countries. Just compare today's generation with older generations.

My father was significantly older than me. He didn't have electricity early in his life. He didn't have comforts like an electric fan till he was in his teens. He could afford air conditioners only when he was in his 40's. When he was younger, smallpox was a constant presence in society (measles is nothing in comparison). He went from being close to food insecurity to not having to worry about food and shelter. I could make a really long list.

Now while in general he was a content person, at times it was clear that all these gains (with the possible exception of not having to worry about food and shelter) played little role in his mental happiness. As society progressed, the reference points all got reset.

This isn't all that different from comparing rich with poor societies. If even in a rich society you find that all these gains (which even the poor in society benefited from) haven't made a big impact on one's mental happiness, one shouldn't expect the same when comparing rich with poor societies.