Gah ... Every so often, I reach saturation point with "Healthy diet just as cheap" threads. I try not to post, but here I am 
I know loads about nutrition, and cooking. I know more about healthy eating than most nutritionists. I was raised by a healthy eating bore. For decades, my food intake was exemplary. Now I am [a] disabled and [b] poor.
Doctors & advisors still find my intake very good. But it isn't, it's adequate. The amount of carbs I shove in my face has exploded. (The amount, not my face!) It is much, much easier to feel satisfied with a ton of carbs. And it's much cheaper.
I can't cook as I used to because of disability. But a parent working inconvenient hours would have equivalent problems. Another reason I can't cook as I used to is that straightforward cuts and fresh veg are too expensive - this also applies to anyone making a budget stretch.
There's a world of difference between making ten different things out of mince for a fortnight, or as a challenge, and eating things made out of mince forever (same if your 'mince' is lentils & beans, btw.) Mince that has 5% fat costs nearly three times as much as 20%. I never have interesting veg these days, and very rarely buy ones that need much preparation - because of time and not being able to afford waste. When I'm hungry, I eat bread and butter/jam. A loaf of bread used to last me a week, now it's two days (and sometimes one.) Cakes have become a regular feature - whether I make them or snarf a £1 bag of mini doughnuts, it's the same: instant satisfaction at minimal cost. It's comforting. My body told my brain, "Get food!" and, fancy that, I didn't happen to have a bunch of highly perishable, expensively healthy items lying around. You have to eat a fuckload of apples or carrots to satisfy hunger. A wrap of chips, on the other hand, will keep you feeling fed for hours.
Experience tells me people will come along to tell me why I'm wrong and what I should be doing. I would gently suggest that perhaps they aren't both time-poor and money-poor; basically don't have a clue.
I agree it's a crime that so many people really don't understand food or know how to cook. But criticising them doesn't help anything; neither does utterly impracticable advice from the well-meaning.
There are a million households relying on food banks. Food banks prioritise high-carb items, in case you didn't know, because we now have folks who are starving. And every body needs calories before worrying about what those calories are made of. There are very many people on tiny budgets who can't access a budget supermarket and have to buy food at expensive corner shops. There are loads with dreadful cooking facilities, and who have to wrangle their kids & shopping up flights of stairs. It's really not surprising that evaluating the nutritional value of everything comes pretty low down the list of priorities.