There’s a big cake mix manufacturing plant near where I grew up, and I knew a lot of people who worked there. They all confirmed that the only difference between the name brand cake mix and the store brand they made was the box they put it into at the end of the process.
From cake mix all the way to advil liquigels, then are almost always packaged by the same manufacturer. Why pay some other manufacturer to set up their production lines to make a generic version of something when the original company will do it for you and has their production line already set up to do everything except stamp their name on it.