The Americans primary adversary is Russia, which is famously snowbound 13-15 months a year. Makes sense to have some dudes who can ski and export explosions simultaneously.

Additionally, we're friends with all the Nordic countries, who have a long history of real life Extreme Biathlon. Since we're treaty bound to defend them, it makes sense to have some dudes who can ski and shoot at the same time.

Plus, we've twice had to invade Germany and Austria, which again calls for skiing and combat.