Earlier quoted context omitted.
It's cheaper to buy fresh food than junk food. If you're buying junk food it's because you don't have a place to cook or you're too lazy to cook.
I'm not sure why you're being down voted here but you're pretty close to correct. There have been many recent studies showing fast food really isn't cheaper than buying other types of healthier food. It is pretty close because there are an incredible amount of low cost high calorie foods like beans, nuts, rice, cheap cuts of meat, the list goes on. Here is one from the UK Economic Affairs: https://iea.org.uk/wp-conte…
I suggest you consider the fact that many people in the US, especially in poor, urban areas live in "food deserts" where there are no supermarkets close by that sell healthy food at reasonable costs.
http://americannutritionassociation.org/newsletter/usda-defi...
If you are poor and have no vehicle you depend on mass transit. This costs both money and time. If you are poor and lucky enough to have a job, its likely to be a low-paying job with a lengthy commute (in terms of time, bus and train transfers, if not in distance). This leaves you very little free time to spend half of a day for a lengthy trip outside of your food desert to get some fresh food. There is also the issue of bringing your groceries home. Have you ever tried to ride the bus or the train while carrying a bunch of packages, especially when it is crowded? How about transferring buses and trains while trying to carrying several packages? Do you have a proper kitchen? Many poor people don't. Proper storage facilities and equipment? Most poor people have roaches.
These are just some of the collective obstacles faced by many poor people in terms of their access to fresh food.