It is because the checks and balances do not work. I know it is hard to believe, but that is the inconvenient truth.
The United States Constitution, and subsequent state constitutions, are not the products of some divine purity that Blind Justice innocently allows nefarious persons to interpret and exploit indefinite aspects. The American charter system is of an antiquated design that was never secured by a practical system of checks and balances. “Fuzzy concepts,” is what we use to describe such vague aspects. It is the founders’ half-truth that they could not avoid, because they did not have all of the information necessary for ordering a more reliable separation of government, and the expansion of the government is proof positive of that lack of information.
There are anecdotes from the founders that suggest caution upon the expansion of the government. This was because the founders did not know how to order the Constitution for expansion because they did not have all of the information necessary for understanding a fully deployed robust government. Nor did they have the HTML formatting technology that is invariably necessary for rendering the cascading hierarchy of directive systems (charter articles) to accommodate the orderly expansion of government and coordination of the balance of power.