The most accurate discussion of why a bill of rights for the national government might not be necessary is:
The national government has only delegated powers.
This argument suggests that because the national government is limited to the powers specifically granted to it by the Constitution, it cannot infringe upon individual rights beyond those powers. Therefore, a bill of rights may be seen as redundant or unnecessary. However, it is important to note that this perspective was contested at the time of the Constitution's ratification, leading to the eventual adoption of the Bill of Rights.