The Founders (OF THE US CONSTITUTION) feared the concentration of power. They believed that the best way to protect individual freedom and civil society was to limit and divide power.
Thus it was much better to have decisions made independently by 13โor 50โstates, each able to innovate and to observe and copy successful innovations in other states,
…… than to have one decision made for the entire country.
As the country gets bigger and more complex, and especially as government amasses more power, the advantages of decentralization and divided power become even greater.