Assuming you read the article, they address that: "She now calls them 'unusable.' She could buy an additional box to make up the difference, she acknowledges, 'but out of principle, I just can’t.'"
As someone who likes to cook, I understand this appeal too. I rarely make brownies (one or twice a year), but when I do, I just go to the boxed stuff. It reminds me of my childhood when I made them with my parents and siblings. I could reverse engineer the recipe to mimic what it does (and probably improve it), but given how little I make them, so it isn't high on my list of things to do. Now if they changed the recipe, sure, that may make me motivated enough to reverse engineer the recipe, but I would still be disappointed.
I think that's what they are going through. Sure, they could figure out what "1 box" used to be, they could go through the effort of reconstructing it with only from scratch ingredients, but that doesn't take away from the fact that it's disappointing to have to go through. Maybe this recipe is one they always made for their kids and now grand-kids.