Nice try but no. Germinated compounds which are self producing do almost all the work and for much cheaper. Cooked meals require all the work of growing and maintaining outdoor processes which can't be controlled nearly as easily, as well as pasteurization in the case of things such as milk, and finally preservation, whereas raw nutrition breaks down - if at all - far slower than more organic compounds. A better answer would have been because of social convention, lack of proper jobs, or even because people would dislike the taste