You can’t feed corn/soybeans etc. to people ?
I suppose if you were to strictly follow FDA guidelines for US distribution that may be true for some grains, but it certainly isn’t true in the third world, where human and animal feed grains are completely interchangable. Whole corn is whole corn to a Mexican peasant. You can feed it to your kids or you can feed it to your chickens.
Other items like some protein meals, cellulose like in hulls, etc. are not human edible. But this stuff is a minority of feed bulk.
Those people just won't get even close to the same nutritional value out of it as grain of higher quality that would be wasted (and unprofitable) as livestock feed. The quality of soybeans, wheat, and corn used in livestock feed is nowhere near the quality of soy, wheat, and corn used for people, FDA guidelines aside. It has more to do with soil and climate, and the protein they can impart into the grain, than FDA guidelines -- this is what grain farmers have told me with regard to who they can sell to, and get the highest price for, their crops.