Those are extremely recent ancestors, from less than ten thousand years ago. Moreover they were located in a place (the Andean highlands) where it is likely that there were not enough animals to allow them to sustain themselves by hunting.

Our ancestors have shifted to a diet with a large percentage of animal fat and meat, which has lead to a simplification of our digestive system, for more than a million years.

Only during a little more than the last ten thousand years there has been a reverse shift towards a lower percentage of animal food, most likely after we had exterminated most suitable wild animals, which forced us to become creative and discover agriculture, otherwise we might have become extinct, like our prey.

Now, with our reduced digestive system, we could not live eating the kind of plants eaten by a gorilla or even by a chimpanzee. We need much more nutritious food, which can be provided only by plant seeds, the only parts of plants that are rich in proteins.