If you believe that anyone counting cents is aware or concerned with it being "rich in protein" by your standards then count yourself among the disconnected. Survival is first.
I used to volunteer to feed the homeless vegan meals in downtown LA and also spent 2 years volunteering for a vegetarian soup kitchen in Copenhagen. Clearly you are the expert on the matter and I'm clearly the one "disconnected" from reality.
I don't know why we blame the poor for this but a bad diet is quite literally bad macro economics and good micro economics for the companies making the profits.
It's especially bad with all the fake/bullshit nutritional science that has to be debunked which created a whole weight loss industry.
Shitty refined carbs and sugar/corn syrup might save you money over the short term but over the long term you're going to pay the price with massive health issues. Considering most poor people's greatest asset is their own body that's false economics.