Because our country is a geographically large entity with far ranging differences between the population in various areas I believe that one Federally imposed solution may not be the best answer.  What works well for the Northeastern area may be inapplicable to Alaska, etc.

In addition, the state governments have a smaller entity to deal with and a better chance of making sure the policies are kept in place, to evaluate their effectiveness and make changes as needed.

One blanket rule is not always the best solution.