Dread is a better conduit for fear for movie audiences than gore will ever be. When gratuitous blood and glistening entrails become the point of a scene, audiences go into defensive mode. We immediately judge the scene - and the movie - by whether it looks fake or not.
The harder a horror thriller works to be shocking, the less successful it usually is. That's why the Freddy Krueger movies and the "Hostel" franchise feel so campy. Our brains won't allow those bloody narratives to become a threat in the real world we should be remotely worried about.