Because it's an asynchronous call. It's delayed until it can happen on all connected clients.
Simply put, how would you sync what you are about to do after instantiating the object? With Unity's networking you get a reference back. Great -- now you are using it. Great as well -- except that what you are now doing with this reference only happens on the client you've instantiated the object on, but not on the remaining clients. See the issue?
You don't need to "find" anything. Change your logic so that whatever you are trying to do happens in a script attached to the object you're instantiating. This way it happens on all clients properly.