Foods have been modified to stay fresher and be more nutritious. But you don't see them in stores.
This is a case of GMOs to preserve freshness, rather than nutrition.
That said, the cost improvements in food aren't such a big impact on real hunger. When people are too broke to eat, making food half as expensive really doesn't have that much impact. And much of the savings-per-calorie relative to fresh food get factored into profits.
Food deserts are a huge problem in this country - places where there is no access to fresh food. They don't happen because junk food is cheap, but rather because it's stable. Fresh food can be just as cheap, if you can keep it flowing.
You're not wrong about the lack of advances in genetics arriving in markets. What I think you've overlooked is that between attacks on the business models that make such advances possible and the political cover that such attacks bring to the "DON'T EAT THE SCIENCE" people... this isn't likely to change. So please, don't complain about the lack of advances in genetics until you're prepared to stop giving cover to the Luddites ranting about frankenfoods. Proposing a different - and practical and workable - business model that allows for the commercial development of GMOs without abusing copyright would be a great way to go about this.
Also: look up Golden Rice. More nutritious foods have been made. And the lock-in angle addressed. Yet the stuff is still not widely grown.
Your reading of food deserts is naive, however. Junk food isn't just cheap in money. It's cheap in time, infrastructure, and required knowledge. A burger from McD's is cheap, hot, and instantly edible. Even the cheapest of Healthy Fresh Green Things requires time to cook, facilities to cook in, equipment to cook, the knowledge to cook, and a place to store the results.
You cannot just put Healthy Fresh Green Things in food deserts and get results. People have tried, and the stuff rots on store shelves.
I completely and utterly disagree that I'm "giving cover" to the people that I called (and you quoted) "DONT EAT THE SCIENCE". That's open mockery of their Luddite ways, and I come down hard on them in these discussions. I loathe their ignorance-wrapped-in-smugness attitude. But by the same token, I have no love for the people who love GMO because "It's SCIENCE!" (you know, the ones who downvote my comments on this subject), without thinking about what problems they're actually trying to solve.
Solving problems that don't actually exist is why many startups fail. There's indirection going on here. As I've said repeatedly, the problem GMOs solve isn't food supply, because we don't have a food supply problem. The population of the Earth has doubled in 50 years, and food costs have dropped 50% over that same period. Does this sound like desperate measure time? No, it sounds like what we've been doing has been tremendously successful at making food more available and less expensive.
So the the problem GMO solves isn't making more food - it's making more money for Monsanto. Is this what we really want as a society? More concentration of wealth and power in the hands of a business model that can and does buy governments? For all the self-styled libertarianism around here, people sure are eager to hand massive corporations that don't act in their interests even more power. Me, I think that's stupid.
Again, what problem are you trying to solve? And does that problem actually exist? If you start with a solution that stimulates your nerd fantasies, and then defend that solution instead of reframing the problem, you're probably wrong.
Loss of biodiversity is an observable problem. Monocropping damaging the soil is an observable problem (and is nitrogen fertilizer and Roundup a solution?). Cash crops bringing outside money and political abuse into developing countries is an observable problem - one far more directly involved in third world hunger than crop yields. I'm after the real problems of the food chain. Are you?