Quote Originally Posted by antisocialmunky View Post
... You can put pockets on anything. Its like... you sew a patch of cloth onto your choice of clothing and you has pocket.
Sure. But are the other garbs with pockets on - these days, mostly jackets etc. - even half as convenient and "always with you" as pants ?
You could probably figure out other ways to prevent frostbite but the amount of surface area pants provide isn't exactly helping you conserve heat.
OTOH you can ensure your legs and groin alike are more or less all the time properly insulated from the cold, protected from direct contact with snow and simply the cold air, to a degree at least shielded from getting wet, there's an extra insulating layer over them... all without having to meaningfully sacrifice mobility, the arc of movement of your legs, having a really heavy long coat hang from your shoulders (though in really cold weather people don a greatcoat for extra warmth, natch), and so on and so on.

There's good reasons why trousers, or shorts-and-hose arrangements largely similar to them in practice, have been so darn popular in the northern parts.
...also, since when did the Celts and Germans and whoever pick up trousers from the Iranic nomads ?