They probably didn't like "factory-made" capitalist stuff.
My 6-month old granddaughter has been on soy formula since her first few weeks after she showed signs of lactose intolerance very early. The kid has thrived on that stuff and looks like a little sumo wrestler. A very healthy and happy baby. But soy infant formula is fortified with the kinds of vitamins and minerals an infant needs in their diet. These moonbats probably just went to the health food store and got soy milk made for adults.
Since a lot of vitamins are made from animal byproducts, I bet that’s much of the reason behind why they avoided the formula. Unless the soy milk they were giving the baby was indigestible, the baby may have survived if there had been some form of sugar added & while apple juice would have some, there’s no way it had enough & it gives some infants diarrhea. Don't try this at home folks. A pediatrician should be consulted.