It’s because mild climates have bad insulation and when it’s 5C out moving the thermostat from 17 to 21 is a big change.
When it’s -25C out, not so much.
Japan can actually be a case study of that: detached homes on Honshu (the main island) generally have poor insulation, in winter they tend to be quite cold and spot-heated (using kotatsu and kerosene space heaters, with heavy clothing).
On Hokkaido meanwhile, good insulation (including double or triple pane windows) and central heating are common (the island has insulation regs and there are loans dedicated to properly protecting against the cold), and inside temperatures tend to be cosy. It’s a regular occurrence that Hokkaido residents catch colds when visiting tokyo in winter, because they don’t have the habit of bundling up inside.
Though when it comes to Honshu, one of the justifications for the lack of insulation is the difficulty of keeping indoors drafty and dry during the extremely wet summer, to avoid the walls outright rotting on you.
When it’s -25C out, not so much.
Japan can actually be a case study of that: detached homes on Honshu (the main island) generally have poor insulation, in winter they tend to be quite cold and spot-heated (using kotatsu and kerosene space heaters, with heavy clothing).
On Hokkaido meanwhile, good insulation (including double or triple pane windows) and central heating are common (the island has insulation regs and there are loans dedicated to properly protecting against the cold), and inside temperatures tend to be cosy. It’s a regular occurrence that Hokkaido residents catch colds when visiting tokyo in winter, because they don’t have the habit of bundling up inside.
Though when it comes to Honshu, one of the justifications for the lack of insulation is the difficulty of keeping indoors drafty and dry during the extremely wet summer, to avoid the walls outright rotting on you.