Well Black Ops 2 basically equals Future warfare. Why is it always the Russians? This is somewhat interesting since it's in the future. I think FPSRussia also has those 4 rotor helicopter with a machine gun on it.
If the enemies were:
Africans: It would be considered racist
Europeans: We're betraying our allies
Americans: Considered unpatriotic
Middle Eastern: Here we go with the 9/11 thing
The Russians are manly enough to participate into being the enemies