The rest of your numbers are similarly off: - you are giving each happy meal 1.25 lbs of potato!? - apple serving size is 1.2 ozs - An average apple is 8-10 ozs, 4 apples = 26 happy meals minimum.
You realize how expensive fast food is if you are at all used to cooking at home from scratch all the time.
But cooking from scratch all the time has a time cost, too. Many families are time poor as well as money poor so there's a balancing act to be done.
For the burger example: buying pre-formed burger patties is still massively cheaper. Throwing a pre-formed burger patty from your fridge in a pan and putting it on a bun with a slice of cheese will take you ten minutes. Microwave small potatoes while you fry. You are done. There is no prep, you have made 1 easily washed pan and bowl for potatoes and your plate.
Is it the exact same thing taste-wise as your fast food meal? No, the potatoes aren't fried, sorry. Does it hit all the macro nutrients for far cheaper, and probably less time than even going to the fast food place? Yes.
Tots > Fries
$4 for 2lb ground beef
$3 for 10lb russett potatoes
$4 for four apples
$4 for a 52oz jug of OJ
$18 total for ~8 "Happy Meal equivalents", or $2.25 per meal, so less than the actual Happy Meal, but you need 1. $20 cash to buy the supplies and 2. the time/equipment/knowledge to prepare the meals.
Yes, the headlines are rage-bait, but fast food is still ridiculously inexpensive. Yes, you ca reproduce the fast food at home, or live on rice+beans, for less. But add some quality protein and a pile of fresh veg and the price goes up.