Why can't FBSDKGraphRequest use from the main thread?

Question

When I put the Facebook Graph API on a work queue, it does not return. Any idea why? It would be easier to write code without putting it in the main thread. I would not put up calls if I need "me / friends" and "me" too.

let gr = FBSDKGraphRequest(graphPath: "/me/friends", parameters: nil) gr.startWithCompletionHandler({connection, _result, error in