Well 1, it's not the federal government's job to do that. The state governments can do that if they want, but the Constitution doesn't permit the Feds to regulate food.
Allow me to repeat. We are not a country of laws, but a country of political will. This is why libertarians will never win or be relevant.
The Constitution also does not allow for corporate welfare, but we have it and it's not going away. Putting rules and regulations on how taxpayer money is used is not bad policy.
This is like complaining that it's unconstitutional to regularly drug test food stamp recipients. You've just entirely missed the point. Probably on purpose.