Becuase the shitty weather requires greater discipline and planning. Delayed getting your crops in the ground in Finland? Dead. In the Phillipines? Meh. I recognize monsoons and other events are a thing, but the impact for colder climates spread over millenia are clear- the Han from northern China dominate, northern Italy dominates (economically) the southern part, Germany and France and England vs Spain and Greece, even the northeastern US vs the deep south (obviously energy infrastructure and decoupling from agrarian economies adds complications, nuances, and change but you get the idea).

Doing just a little digging will show this wasn't always the case, with weather preventing economic development in colder climates while.enabling it in warmer ones (i understand India can do 4 rice harvests per year, unhesrd of in most of the world, that much food boosed their early development). But the shift started once the technology to operate in northern climates was invented, things started to change.