Originally posted by Achivai:

I think it's BS as well. Why can't I make a cold-resistant fur from deer and boar hides?

Because their hides aren't insulated enough for the extreme temperatures of the higher elevations of the mountain biomes.

Or better to say, because of the gear progression in the game, it is an incentive and challenge meant for the biome to use materials from more challenging creatures in the progression of the game.