Who says? Certainly not the Constitution. Research into the intent and understanding of the Founders and Ratifiers shows they expected all three branches to participate in constitutional knowledge and interpretation.
The Supremacy Clause does not say the rulings of the Supreme Court are the law of the land but the "Constitution and the Laws of the United States which shall be made IN PURSUANCE thereof" (Art VI Sec 2).
A very, very odd attitude to my mind. You seriously want to give Congress the power to essentially rewrite the Constitution via mere laws?
You can’t see any particular problems with that approach?