In a lot cases violence is not as necessary as it is used. The usage of violence is often just for aesthetic purposes with little implications on the deeper game mechanics or story (unless the experience is meant to be realistic, horrific, etc). It's usually just the outer shell of the game and a lot of it can be removed without harm to the core experience.
I personally don't mind if there's violence or not (unless its excessive), but I do understand the need to reach as broad of an audience as possible; and it can be quite rewarding to successfully pull off various themes and experiences without settling for violence. I have seen this done successfully in only a small number of works, but I must admit I have a different sort of appreciation for those works compared to works that settled for violence as the vehicles of their experience.