Your examples are different.
The North - in our Northern hemisphere setting - is colder, and cold symbolizes death in a lot of our cultures, simply because winter means death :
- People becomes sick or die form the cold
- Food becomes scarcer.
- Plants die, including crops
- A lot of animals die, hide, hibernate or just leave until it's warmer
- The Sun doesn't rise as much as usual which make the days shorter and darker.
Regarding the Sun, since our ancestors depended on astronomy to subsist and especially the Sun - which was quite bound to the activity of growing stuff - and it translated with that celestial body being overly represented in spiritual matters. Therefore, both the declining appearance of the Sun and the shortening and darkening of days filled them with apprehension and even fear. Many religions considered winter and especially its solstice as periods during which the realm of the dead was particularly close to ours - think about the Celts with Samhain for example.
Also, humans themselves become cold and pale/blueish when they die.
Therefore, you can draw relations between Winter and the frosten carpet it lays on the world as symbolising the opposite of life.
The North is hardcore Winter. From a Southerner point of view, the North is always cold and a freezing wind sometimes loaded with snow often comes from there. Moreover, overcome your fear and push even further and you will stumble upon places where winters are month long nights. It may seem to anyone who doesn't know better that that's where the dark and cold forces that are manifested by Winter are actually living. That's more or less the case in aSoFaI, by the way...
But most people never went to the North, and therefore didn't know what was there, they could only assume things.
But you question tackled that issue in the literary world. Although novels are inspired by our world, they follow other rules.
The freezing North is far less hospitable than the more temperate areas that are... well, not freezing... Therefore, novels usually have people thriving in temperate areas and nothing much to put in the freezing regions, which become even better place to put the evil villain, dark lord, dead god or whatever gloomy, creepy and dreadful antipathic warlord is threatening your people. Because that's the whole point. When you write fantasy - or something closer - the exterior enemy of your people has to be close enough to be threatening but at the same time living in a region where your people has no incentive to be.
You'll have to agree with me there, the dark lord from the sunless valley between the frozen mountains gives more chills - sorry... - than the dark lord from the evergreen hill nearby the singing spring.