The reason is that you would be trading off the name and good will of Quaker Oats in trying to entice people to buy your product. However, if all you wanted to do was use the ingredient (without the advertising component), you could walk into your local supermarket, buy the stuff and use it.
However, if you contacted Quaker Oats directly to work out an arrangement, you might get a better wholesale price.
Nina L. Kaufman, Esq. is an award-winning New York City attorney, edutainer and author. Under her Ask The Business Lawyer brand, she reaches thousands of entrepreneurs and small business owners with her legal services, professional speaking, information products, and LexAppeal weekly ezine. She also writes the Making It Legal blog.