system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] why do some jedi corpses vanish (like Obi-Wan or Yoda) but others don't? (like Qui-Gon)
gpt
When a Jedi dies, their spirit is not destroyed. Their spirits become one with the Force. The Jedi believe that this process is helped along by the destruction of their mortal body which ties them down, and that's why they would always cremate their members. There is, however, an ancient technique in which a Jedi can prepare themselves for their death before the death actually happens. When a Jedi who has used this technique dies, their body dematerializes and their spirit joins with the Force immediately. Howver, Jedi who use this technique are able to maintain their identity separate from the Force (for a time) and therefore gain the ability to appear as a Force Ghost, and speak with the living. Very few Jedi were known to do this, and the technique had been lost for thousands of years. Qui-Gon Jinn actually managed to rediscover it, and shared the technique with Obi-Wan and Yoda after the Clone Wars.

It's unclear as to why Qui-Gon Jinn's body didn't disappear like the others did. He seemed to have trouble with communicating with people at first, as evidenced by the fact that he didn't make contact with anyone until around the time of the Clone Wars, specifically the fact that he didn't appear to Count Dooku as he was falling to the Dark Side. It's possible that because he had just rediscovered the technique he wasn't *entirely* set on the details, and had to figure some of it out by trial and error, which took his spirit time. This is all speculation, though.