Because they're not actually "overpriced"? A BC chocolate cake mix costs $2 at my local store. Let's compare to a cake recipe using ingredients from the same store and using this recipe [1] and this weight conversion chart from the recipe authors [2]. For grocery prices, I'll be picking the "normal" size item as if you were stocking a kitchen pantry (e.g. the 5lb bags of flour and the 4lb bags of sugar, not smaller "half the amount for twice the price" packs, but also not bulk packs).

* 270g flour: 65¢

* 6g baking powder: 10¢

* 3g baking soda: 1¢

* 4.5g salt: 1¢

* 64g cocoa: $1.15

* 354g sugar: 90¢

* 113g butter: $1.42

We'll skip the vanilla, milk and coffee in the KA recipe on the view that we're substituting for Betty Crocker cakes here, which aren't likely to have coffee and vanilla extract in them.

Both recipes require the baker to supply eggs and oil. KA wants less oil but one additional egg, the BC box mix wants more oil but one less egg. Calling it a wash here.

So the total cost for our home made cake, using just the portion of the ingredients that you (should) already have at home is: $4.24, over 2x the box mix. Even if you take out the chocolate and go for a plain vanilla cake, you're still taking $3.09. That KA recipe might taste better (in fact, it probably does based on my experience with KA recipes). But I'm not sure it tastes so much better that I wouldn't rather save the time and dishes.

[1]: https://www.kingarthurbaking.com/recipes/chocolate-cake-reci... [2]: https://www.kingarthurbaking.com/learn/ingredient-weight-cha...

The 15oz (pre-shrinkflation) Betty Crocker mix weighs 432g, 2/3 the weight of your recipe's flour and sugar alone, so your recipe is for a much larger cake.

Wal-Mart's own brand flour is about (Canadian) $C0.15/kg if buying 2.5kg, cake & pastry flour more like 24 cents/kg. Granulated Sugar is C$0.15/kg. I'm not sure where you're buying flour & sugar.

Your most expensive ingredient is butter but you could have easily chosen a recipe without butter. I reckon the cake with butter will be much better than BC's version though.

Other advantages of baking with a recipe are being able to scale the recipe up or down as needed, and always having the ingredients for many different recipes on hand without having to buy a vanilla cake mix, a brownie mix, a pancake mix, a waffle mix etc.

The main advantage of a recipe is tweakability. I find most commercial cakes far too sweet, and when I bake from a recipe I can find the point to which I can reduce the sugar without it becoming too bland.

I don't know whether they're harmful but I'm quite happy to cook a cake without Propylene glycol, Xanthan gum, cellulose gum, sodium stearoyl lactylate, monoglycerides, and monoesters of fatty acids

I've always been baffled by the popularity of pre-made recipe boxes. Maybe useful if I was camping or something, but not when I have access to an actual kitchen.