Since the Constitution acts directly on both the people and the states, both must be represented in the lawmaking body of the republic.
It really is as simple as that.
That's the single biggest misconception of how the Constitution was intended to work.
The only 'people' directly under the Constitution were the ones inside enumeration jurisdiction, such as in the federal enclave, where the federal Congress was supposed to act as a city council, or municipal entity.
James Madison Federalist #43 -
The extent of this federal district is sufficiently circumscribed to satisfy every jealousy of an opposite nature And as it is to be appropriated to this use with the consent of the State ceding it; as the State will no doubt provide in the compact for the rights and the consent of the citizens inhabiting it; as the inhabitants will find sufficient inducements of interest to become willing parties to the cession; as they will have had their voice in the election of the government which is to exercise authority over them; as a municipal legislature for local purposes,
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Outside the areas of enumerated jurisdiction, the Constitution operated ONLY on the entities of the States, NOT on the People IN the States. To do so, in fact, was considered treason.
In the United States of America the people have retained the sovereignty in their own hands: they have in each state distributed the government, or administrative authority of the state, into two distinct branches, internal, and external; the former of these, they have confided, with some few exceptions, to the state government; the latter to the federal government.
Since the union of the sovereignty with the government, constitutes a state of absolute power, or tyranny, over the people, every attempt to effect such an union is treason against the sovereignty, in the actors; and every extension of the administrative authority beyond its just constitutional limits, is absolutely an act of usurpation in the government, of that sovereignty, which the people have reserved to themselves.
Preliminary Remarks, St. George Tucker, View of the Constitution
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The State entities are the proxies that were SUPPOSED to stand between the People and the federal government and act as a Constitutional buffer to secure our Liberties.
The fact everyone seems to believe the federal government can control the entire country at will is the main reason tinkering with the Constitution is pointless, IMO.