Most of Eurasia is like that with several hundred million people living in regions with harsh winters.
Where would you re-settle four hundred million people?
Would they want to be unwelcome guests anywhere else?
As a species we lack fur, so we are really vulnerable to cold.
>Where would you re-settle four hundred million people?
No one is talking about resettling anyone. My question was just about why people individually choose to remain in places that feature temperatures well outside of the range compatible with our species. Others have covered it pretty well. Some combination of habituation, laziness and disliking hot summers basically.
People have been living in those cold climates long, LONG, before modern heating systems. More than "laziness and disliking hot summers" I would say that humans will settle wherever are resources that can support them, period.
An individual might move but that doesn't affect the topic we're talking about.
Also, moving is not easy: you have to learn new languages, acquire skills you did not have use for previously, and get a work permit.
(And for the hilarious part, we often see people from warm countries moving to more temperate ones because those are economically and politically better off)
As a species we lack fur, so we are really vulnerable to cold.