The Forgotten 10th Amendment

From the Whig:  http://whigblog.blogspot.com/2009/11/forgotten-10th-amendment.html

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people. -- Tenth Amendment to the U.S. Constitution

The amendment states but a truism that all is retained which has not been surrendered. There is nothing in the history of its adoption to suggest that it was more than declaratory of the relationship between the national and state governments as it had been established by the Constitution before the amendment or that its purpose was other than to allay fears that the new national government might seek to exercise powers not granted, and that the states might not be able to exercise fully their reserved powers..... United States v. Darby, 312 U.S. 100, 124 (1941).

In effect, the U.S. Supreme Court has decided the 10th Amendment to be a nullity, which adds nothing to the Constitution. As an amendment, and part of the bill of rights, one would think it would be as important as any other part. But that is not how Supreme Court decisions view it. How did this happen?