It’s a common question, and if you satiate your curiosity with a quick google, you’re likely to find answers swirling around viral challenges, the smash hit of Hot Ones, etc.
But en-spice-ification is also a phenomenon in modern China too, and here there’s no Hot Ones, nor are their artisanal hot sauce makers at the farmer’s markets. Two very different countries, same trend.
In the linked post, I do a little theory-crafting. I’m not sure to what extent I’m content with my answers there, but what’s undeniably true is that the road the chili pepper took to national domination were quite different in these two respective countries.