> was it supposed to be mostly a coordinating organ leaving the states to be much more independent?

I guess my functional question is why agriculture requires federal regulation to the tune of the USDA. (And I'm asking this genuinely. As a not farmer.)

$189 billion of USDA's $213 billion budget is the Food and Nutrition Service. They're administering SNAP, WIC, school lunch programs, etc. These jobs are policy, distributing money, coordination with state programs, etc.

There's a different answer "why" to each of these programs' origin stories, but in general, they were a response to issues that previously existed and weren't being addressed. e.g. the school lunch program was created because we don't expect children to skip meals at school due to their parents inability to provide for them. And it was done nationally because many states failed to solve the issue themselves.

The entire point of the Constitution was to concentrate more power in the Federal Government because the structure we had under the Articles of Confederation was an unworkable mess.