Larger farming operations (with enough production and income to potentially support any advertising expense at all) generally don’t sell directly to the public the way a mom & pop operation might do at the local farmers market…so they don’t need to sell John Q. Public on their products…they just need to sell themselves to the stores so that they are available for the consumers who ARE interested in buying healthy foods.
Earth Fare is an exception, but most grocers will get a particular product from one supplier…for instance all their oranges from one grove…so the choice isn’t the end consumers directly.

The people who really WANT to eat healthy and are committed to do so will seek those products out without seeing an ad on television showing a cut open watermelon or plate of steamed asparagus. Everyone already knows about these foods…it’s just a matter of if you choose them or not. So the return on investment wouldn’t be nearly as great for an organic farmer to buy a tv spot as it is for Sonic.