Why was there no orcs or other creatures of evil within emyn muil?

In the fellowship of the ring, can't remember the name of the chapter so can't cite a source, but Aragorn confirms that orcs hold the eastern shore of the Anduin which isnt surprising , but what is surprising is that when Frodo,Sam and Gollum go through Emyn Muil not a sign or trance of any orcs or creatures of Mordor.

Is there any evidence which might suggest to why there isn't any orcs or evil creature's within Emyn Muil