It is because immigrants are bad

As usual, the immigrant haters are asking the wrong question. The question should be "Why don't enough Americans want to sign up?" not "Should we ask foreigners to fight for us and give them citizenship?"

BTW Ice, why wasn't your grandfather fighting for the Italians?

In Britain, we have done the reverse, drafting people into the army and then refusing them a passport. A famous example is Spike Milligan who served in the artillery during WWII but was refused British citizenship because he was born in India and his father was Irish. So we have someone who served in the army, was wounded in action, whose father was only in India because he was serving in the British army, who is seen by many as the founder of modern British comedy not British enuogh to get a passport. Makes me proud to be British.

Wiki biography