The US isn't a federation of dozens of nations.
This country was never intended to be ruled under a single unitary code of laws.
Weird that the Constitution is the supreme law, then.
The United States more like the EU a union of sovergn states. The states (Original ones) predated the federal government and as such the federal government is the child of the states not the other way around.
The 13 colonies that founded America were not sovereign states prior to founding the US. They were colonies. They became independent by founding the United States and winning the resulting war. And they added more states by conquering, murdering, and colonising their way west.