Oh, that one is easy. The original US constitution gave the federal government the right to preempt state laws in matters within its enumerated powers, but placed strict limits on what those powers are, and created a check against federal overreach by creating the US Senate, which originally had its members elected by state legislatures who would thereby send Senators disinclined to let the federal government usurp their powers.
Then populists amended the constitution to cause US Senators to be directly elected, and since US Supreme Court Justices are confirmed by the Senate, that in turn allowed them to replace the Justices with ones who would do things like read the inter-state commerce clause as covering non-commerce happening entirely within a single state.
Having eliminated any meaningful constitutional restrictions on federal power, federal officials were then captured by large corporations to enact federal regulations that only those large corporations can comply with, and to erode any federal constraints on corporate mergers while still preempting the states from imposing them either.
You can't give the central government the authority to do something and then expect them not to. If you don't want them to do something, you need something actively constraining them from doing it. Which was the US Senate until it wasn't.
