[anonymously]

Because, different diets and foods agree with different dogs. There is no one perfect food for all dogs. Raw is not worth the risk, in my opinion.
Be glad your friend has found a food that his dogs appear to be doing well on.
Hope this helps:

https://www.mspca.org/angell_services/choosing-the-right-diet-for-your-pet/

http://support.mspca.org/site/PageServer?pagename=latestnews_GenericPetFoodRecipes