How could Anakin automatically become a Ghost without training?
Qui-Gon secretly studied alternate emphasis on the Force so as to be prepared to retain some degree of consciousness after death. Maybe this is what he meant by the Living Force (as opposed to the Force).
Obi-Wan and Yoda spent their entire exile mastering it too.
Anakin simply dies, without Force Ghost training, but maintains his identity in death. How?
My guess is that The Chosen One would naturally have this ability. In essense, an ability to cheat death. This is ironic given Anakin's futile attempt to discover the secret to cheating death, not realizing that he had the ability all along if only he would have nurtured it.
Obviously Qui-Gon tried to communicate with Anakin in Ep II, telling him to stop his attack on the Tuskens but Anakin's anger and ignorance make him insensitive to messages from the afterlife. Yoda's force sensitivity is the next best thing as he picks up on it. And Luke's innocence, force potential, and open-mindedness make him immediately receptive to messages from the netherworld of the force.
Make sense? My guess. And yes this is a IV-VI posting really. Not a prequel question. Dont jump my nuts for it.