Very hot climates have jungles that are difficult to clear for agriculture. Also, it's difficult to work energetically in intense heat.
That's why northern Americans and Canadians are more energetic and hardworking than average southern Yankees, if you will.
The distribution of developed and developing countries is influenced by a variety of factors, not just climate. While it is true that colder regions may have had historical advantages for development, such as access to resources like coal and mineral deposits, the correlation is not absolute. Development is a complex process shaped by historical, political, economic, and social factors in addition to climate.
My dad actually brought this up to me the other night. One theory says that countries near the equator do not have seasons or conditions good for farming and agriculture. This was a major stage in advancement in human history. Because agriculture was such a valuable stepping stone, it is possible that it has caused developing countries to continue to struggle today. Granted, this is only a theory my dad heard over the radio.
Its because human brain can function more effectively in cool places. For example, a man can perform any skilled work in an air-conditioned room than in a room with room temperature. So as a result the people who live in cold region of earth can perform any type of work well than the people who live in warm regions of earth. That is the reason why most of he countries on cold region of earth are developed.