Why does policy making in the U.S. include state and local governments?

Question

Why does policy making in the U.S. include state and local governments? What are the common reasons offered for dividing policy authority between state and central government?

Answer 1

State and local governments constitute the US as a whole. Thus, policies made in the national level considers the local governments for its effect and implementation. The Constitution provides that the government must look into the welfare of the local governments in the making of laws.

Answer 2

Because we are a federation. Smaller local governments are considered more responsive to the citizenry.

Remember, 13 DIFFERENT colonies had to decide they wanted to work together, and they did NOT want to give up their 'own ways.'

However, things like defense of the nation and foreign policy were considered better nationalized.

Answer 3

It seems to me it is better for local people to decide local issues, every state doesn't have the same people or cultures.
If you have D.C. making decisions for MN, then are MN interests really protected?