Scientifically, as read in Xmas Specials section in The Economist, my theory seems to be confirmed:
The reason may be that capsaicin excites the trigeminal nerve, increasing the body’s receptiveness to the flavour of other foods. That is not just good news for gourmets. It is a useful feature in poor countries where the diet might otherwise be unbearably bland and stodgy.But I need more convincing empirical finding, and maybe household survey data could help by showing the relationship between chillies consumption, or purchase, to total income --presumably after controlling the price.
Yet, even if I am right. How could you tell why, as the article suggests, that, thanks to globalization, people in developed countries start to embrace chillies?
Then perhaps, I need to resort a second speculation: The food in developed countries are even more bland than in developing countries. So bland that it cancels out the income effect.