Because they have no or smaller cheeks. But they have very acid stomachs.
The Comparative Anatomy of Eating
http://www.vegsource.com/news/2009/11/the-comparative-anatom...
Omnivore or Herbivore?
https://livinontheveg.com/omnivore-or-herbivore/
Milton Mills, MD: Are Humans Designed to Eat Meat?
https://www.youtube.com/watch?v=sXj76A9hI-o&t=66