It took Qui Gon the time between PM and AOTC to become a voice heard by Yoda and he can't appear as a force ghost. Anakins body doesn't disappear and he receives no training, Yoda and Obi-Wan achieve the feat with years of training in exile while they are alive. It's strongly implied that it's a feat one achieves on their own after extensive training hence Yoda's line "training I have for you" if they could achieve it after death in the time it takes Luke to get on Endor and join the celebrations why would Qui Gon go to the trouble of making contact while they are alive and training them in the first place ? He could just wait till they pass away and show them in the great beyond, like as you say Obi-wan and Yoda do with Anakin. Lucas' after the fact comments aren't cementing anything they're just another example of him trying to paper over another hole in the story.