There are a ton of problems with hand gestures. One, they're hard to see and blocked by line of sight (voice isn't.) Two, they require hands to be free to communicate (not always the case, and in situations of survival it's probably not doable at all.) Three, they're limited versus voice. Voice has soft and loud and more sounds can be made than variations of hands. More meaning can be ascribed to a sound.
The article convincingly argues there's more to this than just your list of problems with hand gestures and the article