Why did this Timber Rattlesnake behave this way?

A couple days ago I was hiking with a friend in Rocky Gap state park on the Evitts Mountain trail. The park is located on the western part of the state close to the border with Pennsylvania. We broke off the trail on the way back down to take a short cut back to our campsite. I was several feet in front of my friend throughout most of the trip. While walking down the mountain I stepped less than two feet away from a Timber Rattlesnake. Once I saw the snake I did what you're not suppose to do and yelled "snake" and put about 15 feet of distance between myself and the snake. The snake was coiled as if it was about to strike but it was not facing me. When I yelled and ran it didn't even seem to notice I was there. My friend and I watched it for a little while. After several minutes of not moving it slowly slithered away. We don't think it was shedding its skin and I don't think it was hunting anything since it slowly slithered away. Why did the snake allow me to get that close but not strike? I thought snakes were suppose to see you well before you see them (especially pitvipers) and move away from you unless they were hunting you. This snake didn't run from me but didn't seem interested in attacking me either. Why was that? What could it have been doing?