When Yoda died he disappeared. But not when Quo Gon Jin and other Jedi were killed. All other Jedi have had their bodies burned. There’s a reason for that that’s more than just ritual. Read on to learn more.
According to official Star Wars Canon, only Obiwan, Yoda, Anakin, and Qui Gon Jin have appeared as Force ghosts.
Why do they burn the bodies?
The key to understanding can be seen in the episode of Star Wars Rebels “Rise of the Old Masters”. In this episode, our team of Rebels, based on leaked intel from a presumed ally, infiltrate a prison where Master Luminara Unduli was being held. During the break-in, Kanan was able to sense her presence, but… something was different.
When Kanan and Ezra arrived at her cell, the saw, not her, but merely an echo of herself. This echo of Luminara sat up and walked back into a casket where her ghostly bones could be seen through the looking glass.
It was all a trap set by The Inquisitor.
This was a great episode, but this particular element highlights the reason why Jedi bodies are burned upon death. What Ezra and Kanan saw was probably an echo of her last moments before being killed. The force can apparently still live within their bodies and be sensed by others (I’m sure there’s a metichlorian reference to this but since I really hate the element of SW, I’ll ignore it). Burning the bodies removes the ability to still sense the Jedi post mortem.
How do they become Force ghosts?
This is a longer question that really just leads to more questions. But there’s a straight forward story.
The last few episodes of Season 6 of The Clone Wars, we see Yoda preparing to undergo the training to be able to live on after death as part of the Cosmic Force. He’s led on this journey by Qui Gonn Jin’s Force… spirit? (Qui Gonn never finished this training and, as such, couldn’t appear visibly, but could still speak to the living). It is through this training that Yoda has new truths about himself revealed to him and where the future of the Jedi (and their demise) is revealed to him.
At the end of Episode III we see Yoda share with Obi-Wan that he has been communicating with Qui Gonn and would train him to do this as well. So this all presumes that Qui Gonn taught/guided Yoda and Obi-Wan to learn how to remain immortal.
Now Vader/Anakin… that doesn’t really fit in this narrative. You have to start telling yourself stories about how this could still be true even though there’s really no explanation for it. But this is Dave Filoni’s response to this:
It’s a bit meta, but… this is all a bit meta.