Because Alexander Hamilton willed it so-- he and the NYC banker contingent that he kept visiting (a 3-day trip) during the Constitutional Convention.
To learn more, much more, read Kenneth W. Royce's "Hologram of Liberty".
We must face the facts as stated by Lysander Spooner back in the 1870's: "The Constitution has either given us the form of government we have, or it has been powerless to prevent it."