Comment by jeffbee

The United States doesn't have a central registry of citizens. New births are supposed to be recorded by local officials, in about 3000 different jurisdictions, and they're only recorded locally. Many of those local jurisdictions are operated poorly, and in some cases they have refused to issue certificates of birth based on race, or other personal grudges held by officials. So we simply aren't in the position to issue such identifiers, and in particular we can't assume that a person without traceable documentation isn't a citizen.