User blog comment:Dolten/Call Of Duty 2 Big Red One/@comment-670668-20100328134657

Big Red One was made by Treyarch, and they pretty much made it a separate game.

I believe Infinity Ward had some clause in its contract that stated that it was the only developer to have numbers in Call of Duty titles. That is why employees at IW got fired up when Treyarch went ahead and made Call of Duty 3.