My first thought is why are people using these box mixes, the ingredients are trivial. There are recipes online that have the ingredients.

The base ingredients for many things are flour, sugar, baking soda, baking powder and salt. -- these are not expensive and are shelf stable. A chocolate cake mix adds cocoa powder. Some need vanilla.

The mix already requires adding rggs and oil.

Mixing it yourself allows way better quality control; they aren't using high quality cocoa or vanilla.