I'm describing the political arrangement that was made in 1787 when the U.S. Constitution was adopted. It established a federal system with power being shared by a national government and the individual states. It was left to the states to decide when, where, and how to hold elections to choose who will represent them in Congress.

"Local control can be preferable to central control" is a general premise that might be true for a variety of situations. I'm not sure what's "fuzzy" about the idea of centralization vs. decentralization. The question arises in education, economics, politics, etc. Decentralization is inherent in a federal system.

Our national government simply does not have the authority to move into the states and run their elections. That would require a constitutional amendment to replace Article 1 Section 4 of the U.S. Constitution.

So, with the understanding that this is purely an academic discussion -- the U.S. federal system being what it is -- local control is more democratic, not less. With each step up in levels of government, an individual citizen's direct influence becomes more diluted. Elections in the United States are very much a local matter. Tennessee, where I live, is typical of many states. Citizens register to vote at their local county elections office. The county elections supervisor is locally elected. Election volunteers from the local community staff the polling stations on election day.

Regarding your question, why are voting laws and procedures different in Colorado and Tennessee? They just are. 50 different states have independently determined their own manner of holding elections. I don't know what else say. Feel free to explain why you believe a homogeneous, centralized, federally-run system of elections is inherently better than a heterogeneous, decentralized, state-run system.