This is the same for many homes in Spain and Portugal too. For most of the year it's warm enough outside and you can be comfortable without AC (especially if you are in an older building with thick stone walls), but then for the one or two months of winter it is so cold inside, even though it may only get down to 10C (50F) outside. Most houses rely on resistive electric heaters (if they have any) which end up being very expensive to run.

I live in a modern house in Northern Europe, and we don't even turn our heating on until it gets below freezing. Because we have good insulation, only then it starts to drop below 22C (72F) inside.