“Makes less money” is certainly one point of view. Another is “makes the food too expensive to afford for many, and shifts more land usage to farming, to make up for the reduced productivity per acre”. It is not even clear that it would reduce the profits of food producers: it depends on the shapes on supply curves. If every food producer is forced to produce food using expensive methods, and people are forced to buy food anyway (as they ultimately must eat), it is very well possible that the profits could actually increase: if demand for food is inelastic, people will just pay higher prices to get the same amount of food, which would only increase the total profits of agricultural industry.
Wheat, corn, and soybeans are heavily subsidized by the US gov't and vegetables are not at all. Every little tiny program to subsidize vegetable growers is picked at every year (happening right now in my state legislature) -- it's always a fight to preserve.
The agricultural lending system in the US is fascinating. Look up Farm Credit Administration. We have a weird and unique system of paragovernmental financial institutions in the US that do farm lending, and even though it's not technically government-backed lending, everyone sees it as such, and so there are some interesting distortions in the market (compared to a more "free-market" system). It does seem quite centered around US gov't subsidies and farm/ag policies.
A single bell pepper today costs something between $1 and $2 where I am. Imagine the government subsidizes bell peppers so that they cost $.50. As a single bell pepper has less than 50 calories, you couldn't base your diet on it, you would still need some more calorie-rich food to actually give you required energy. Since vegetables (except root vegetables) are not calorie-dense, you'd need to eat seeds (e.g. grains) or oils anyway.
That's why, if your goal is to enable the nation to feed itself, you should rather subsidize the staples, not luxury consumption.
Feeding the nation isn't hard. We could feed this nation five times over with the amount of food we produce. The problem is, we'd probably shrivel up and die, because wheat, corn and soy aren't enough to keep a population healthy. We could actually produce more nutrition and calories with a fraction of the land just by switching from corn to oats. But then you'd be producing less, and hence selling less. That's not as profitable!
And vegetables are luxuries in the same sense that "nutrition" is a luxury. Just because humanity has historically had a shit diet (since the adoption of agriculture) doesn't mean it's a great idea to stop eating vegetables, or produce less of them. We get plenty of calories already - too many in fact. And most of the ones we do get are more harmful than good.
It would be better to get people to eat more of those low-calorie vegetables as it would help stem the American obesity crisis. And as we've seen in this report, vegetables already contain fewer nutrients than they did before - a reason to consume more of them, not less!
It can be solved by using less efficient / more complex farming practices which aren't amenable to mass production of monocultures. But that makes a lot less money, so it will never happen.
A different solution would be to pass legislation specifically to protect the nutritional value of our food. But that would just prompt the ag sector to pump the soil full of so much crap to meet the law's requirements that it'll speed up the collapse of ecological systems (in addition to possibly poisoning us).