Well, throughout history, helmets have been configured to make soldiers appear more fierce and daunting. Think of the bascinets of the 14th century with their eye slits and pointed snouts, or the horned kabutos worn by samurai. These were often lacquered in red on the inside in the belief that the red would tinge the face, giving a more fierce appearance. The red lacquered face shields with their fierce scowls served the same purpose.
Perhaps the maker of this helmet thought American soldiers would flee in terror if they thought Darth Vader was after them :lol: . Imagine the look when worn with a gas mask.