I have had friends say it has to do with the Light and Dark side of the Force but Qui-Gon wasn’t Dark or was he?
If you approach Qui-Gon from a certain point of view… maybe?
Didn’t Qui-Gon have some beef with the Jedi Council? So he thought, hey, this kid IS dangerous, and will destroy the Jedi Order for my revenge!!! HAHHA!
Okay, no, I’m kidding. With the OT, it’s implied Light side users can have a peaceful disappearing death while a tainted dark side user must be burned in order to transcend. Qui-Gon doesn’t really make sense. In fact, when I was little, for the longest time, I thought they were burning Darth Maul.
So again, I just think it’s for Lucas’s “everything must rhyme in some way with his previous films” gag.