Just bad shopping.
Same reason people pay $5.99 for a box of "Kitty Litter Deodorizer" when you can buy a box of regular Arm & Hammer for 99 cents. I even buy the carpet deodorizer that comes in the super size box for about 1.50 a box which is just baking soda plus frangrance, which is exactly the same ingredients as the litter deoderizer.
Then there is the kitty litter liners where you get about 8 per box for about 6 bux, but if you buy the super leaf size garbage bags that come out to lay flat, they will fit on the box (you can get these from costco or sam's w/2 huge rolls) for about the same price. I don't use news papers because - well - they leak through.
I can go on and on...