Because the real Vader died at the end of RotJ so Kylo Ren arranged a hologram of his grandpa to get a posthumous award
Which is rather nice of him, I must say.
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Sat 4 Jun 2022, 18:39,
archived)
A much better answer thank you.
Now please make sense of the Starkiller Base 'projection' seen by everyone at once in TFA, and the whole of the following two movies, cheers.
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Sat 4 Jun 2022, 20:11,
archived)
They were all a hallucination by Luke after he ate some Force-sensitive Coruscant space-mushrooms
Trip only lasted 10 mins real-time. Then he sobered up, had a quite nice lunch then fell asleep while watching a scifi film about a planet called "Earth", set in the far, far future, in a galaxy far, far away, on the holoTV.
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Sat 4 Jun 2022, 20:15,
archived)