What an asinine statement. Do you even have a clue where whey comes from? Do you know anything about the very food you consume or that animals consume? Babies are some of the world’s largest consumers of whey protein, without which it would be impossible to mimic breast milk. Milk itself is very complex and when taken apart there are components that are world hundreds of dollars per pound as well as by-products that yes, do go into animal feed. Those same ingredients fed to pigs in China go into foods made by the biggest brands in the U.S.- comes down to cost.
Go learn a little bit about how food is made commercially these days- you’ll be surprised (both pleasantly and unpleasantly) where it comes from.