Because the federal government has no such Constitutional authority. Go ahead and have an amendment passed, if you must. The powers of the federal government are few and defined, but the powers of the state are vast and undefined. That is what the law in this nation is, and it is wrong to twist it to accomplish a certain end.
This hasn't really been valid since
McCulloch v. Maryland.. Actually it wasn't really valid before that as the creation of the First Bank of the United States, for example, showed.
