You assume incorrectly and should read the Information Assurance section on their page: "NSA to secure National Security Systems, which includes systems that h

You assume incorrectly and should read the Information Assurance section on their page: "NSA to secure National Security Systems, which includes systems that handle classified information or are otherwise critical to military or intelligence activities." That does not include civilian networks or non-DoD government networks or any system that isn't designated a National Security System. It definitely isn't "protecting USA government assets" in general.