One theory I read is that hot climates tend to produce more hot or pungent plants, as these chemicals are often insect repellents. And the tropics lack winter,

One theory I read is that hot climates tend to produce more hot or pungent plants, as these chemicals are often insect repellents. And the tropics lack winter, which gives plants an annual break from insects. They're under constant attack, so they evolved more potent defenses. So part of it is just that these hotter flavors are just more available in hotter climates.