There's been some interesting research on what poverty does to a person's decision making ability.
Basically, the more decisions you have to make, the less able you are to make further decisions.
This is why choosing from a menu with lots of items or going shopping is exhausting.
Some very successful people keep their lives very simple. Psychologically, they're 'freeing up' more decision making power for stuff that matters instead of deciding what to wear.
On that basis, people who just buy fast food because it's convenient probably aren't the type who sit down and think 'well, if I just go to the shop and buy bread and salmon, it'll be healthier and work out better value than if I go to maccas'. It's more 'look, I'm juggling too many things as it is. Want food? Just go to maccas'.
Similarly, even people on low incomes can save if they actually looked at their spending and cut back on unnecessary stuff or did stuff more efficiently. But most don't. Part of the reason is that they are so mentally exhausted just surviving that they don't have the capacity to consider the future.
That makes a lot of sense. I've witnessed this with many of my low socio economic, low functioning patients in occupational therapy rehab (most who are NOT cognitively impaired) when being taught basic living skills.
I can only put the passive resistance of many down to it being too hard - when involving more steps that say those of purchasing a steak and some eggs to fry.
The non poor (who can afford takeaway) generally buy it to free up time and are probably the people more likely to be buying Japanese or healthier but sometimes more expensive takeaway.
At the same time I think the wealthier but busy families are more likely to buy some takeaway food and combine it with some of the healthier food they have at home, ie. pre cooked chicken with home made salad.
They generally put more thought into what the family eats even if takeaway makes up part of the diet.
EN710, my sons favourite takeaway, which he buys about once a fortnight, is a Japanese noodle dish ($9). The other that he likes is the Vietnamese rolls sold down the road from us ($6).
He is very time poor and at the moment working so much (mostly away where food is bought on the company account) that he hardly ventures into a kitchen.
He is still slim and fit however, as he's always on the go, and still up early to do his running.
That's after 2 months of eating out or takeaway most nights - mind you still takes great care with his diet and lunches usually consist of a can of tuna or cooked chicken with some fresh salad and perhaps a small wholemeal roll or similar.