http://www.pcgamer.com/middle-earth-shadow-of-war-does-not-support-steam-family-sharing/

Steam Family Sharing was announced in 2013 as a way for friends and family to share their game libraries with one another. There are some limitations, but basically you can give access to your entire Steam library to up to five people across ten devices. Not all games support the feature, however, and according to Reddit, Middle-earth: Shadow of War is one of them. 

"My friend and I alternatively buy all the good games and share amongst ourselves, but this game doesn't support sharing," DoorHandleWalah wrote. "We had to refund the game because of that."