The reason, Zontar, was the luger was crazy fucking overpowered. What was it, 10% chance to instant kill a guy with a headshot? And considering how fast they fired, an army of luger officers was devastating to infantry squads (hence why we all joke about having assault pistol squads because they are hands down the best weapon in the game against inf cause of that stat issue).
10%? Wow, I never knew that 'till know!