I'm not sure what you're getting at with discussing differences between Australia and the US in agriculture, given that the main fact I used was the (obvious actually) point that it's harder to transport groceries without a car. Are you seriously suggesting that it becomes easier to haul groceries around on a subway in the US than Australia? Or that bus service and subway service are better outside of capital cities than in rural areas?
I'm saying that it's easier to
get the groceries outside urban areas, because the trucks that
bring the food into the area don't have the urban traffic to deal with. And Australia stacks import complications onto that. It's easier to go by rail and road from a giant mostly-empty plains region than get things through major metropolitan areas. The situation of Australia's province capitals has extremely limited bearing on some 70% of the United States, because the considerable majority of the US population isn't crammed into hyper-dense mega-cities and our economy has much more food going around, which both lower the bar for the food being in reach.
The point of bringing up the graph being
solely capitals is that capitals are virtually always massive outliers in the problems of population density. And the graph itself shows the
price of the food rising, in a time when Australia's food production
fell. This is a set of variables that describes a reason for food insecurity utterly independent of any "food desert" in that it describes being
priced out of the food due to conditions fairly specific to Australia regardless of open time, and additionally describes a
cause of formation for them, because these impoverished neighborhoods are typically the most densely populated or have the worst road layout or are the deepest in the metropolitan area, in a time with declining supply of food driving up the price, all of which establish the difficulties to be
able to stock those grocery stores.
Did you know that every company that handles cargo by truck in New York City has a budget set aside for traffic tickets? Because it is
literally not possible to get their cargo through in a sane amount of time following the traffic laws properly. This is rather important for perishables like food, and doubly so due to "worker protection" laws that set hard limits on trucker work weeks decided by people with zero experience making routine round trips across half the country. If
multi-million dollar companies can't make sensible time without
routinely breaking the law, what makes you think individual people stuck in the worst neighborhoods can?
The problem has a great deal to do with the cities. Not the failures of the wider economy to provide opportunities for wealth, but specifically the hellish mess that is supplying a major city.
Edit: There's one big thing you still have yet to provide, and that's the work-hours of the poor you're saying can't get ahold of sensible food. This is rather key, because "the poor" aren't a homogenous mass. There's a lot of ways to be "poor", and they usually have little to do with eachother.
Debt spirals, lack of jobs to take in the first place, bad qualifications, a criminal record screwing you out of work, ill-advised purchases, specifically wanting to avoid the hell-hours you mention as preventing the ability to cook and thus being stuck working part-time, and then there's very much
some number who are just lazy freeloading sacks of shit, genuinely mentally incompetent, or drug-addicts who are generally perceived to overlap heavily and round out the very bottom.