There are a couple of plausable reasons.

-Programs to help small and "hobby" farmers, like the university and state extention services, are potential targets for the budget axe. If they have a customer base, they are more likely to be around in three years.
-There are sections of the current administration that are big on what I would call victory gardens. This could be research to determine what percentage of the population is growing their own, possibly for another push to try to get things like chicks and seeds to be allowable items for food stamps. I can remember when I was kid there was debate here in VT if they should be allowed in small quantities.
-The NASS is the Department of Agriculture's census agency. They could just be doing what the law requires them to do.

But of course, as has been pointed out, we already know the real reason. The silent helos will be showing up to give you a bill to pay for your own produce after it has already been grabbed by illuminati agents to be sold to aliens from the planet Vega. After all, they are Vegans.