The reason is that virtually everyone not only indirectly uses animal products, but everyone also consumes some fauna or animal foods, even if inadvertently. Finally, the significant energy and rapid growth requirements of a juvenile animal require food that is very high quality and easy to digest. Carnivorous diet for infants is a necessary survival tactic. And so does every other mammal, whether folivore, frugivore, or faunivore.
Every vegan is actually a faunivore.
Finally, readers should know that every vegan is actually a faunivore because of the inadvertent consumption of insects. The more fruits, nuts, and vegetables in one's diet, the more insects one is going to eat.