Mark Hamill came up with his own, insanely dark backstory for why Luke is like that in The Last Jedi
Hamill asked Rian Johnson if he could make up his own backstory for Luke's misery in the 2017 film, and went about as dark with it as it's possible to go.
Screenshot: YouTube
Mark Hamill was famously not especially happy about the direction Luke Skywalker took in Rian Johnson’s The Last Jedi, expressing—while the 2017 Star Wars film was still in theaters—that he didn’t agree with Johnson’s portrayal of Luke as a guy who’d ever give up the fight, no matter how many nephews he fucked up, or how sweet the local milk at his hermitage of choice. Hamill has, since then, tried to clarify that he holds no personal animus against Johnson, and was saying even at the time that he thought The Last Jedi was “a great movie.” But his dissatisfaction with Hermit Luke has long been enshrined into the mythology of hate certain corners of the hideous and leviathan Star Wars fandom have brought to bear on Johnson’s film. God only knows, though, how they’d have reacted if the director had gone with Hamill’s idea for why Luke is so sad when we meet back up with him in the movie.
This is per an interview Hamill gave this week to Bullseye With Jesse Thorn, in which he expressed some regrets for speaking up about his unhappiness during the film’s press tour (“Maybe I should have kept that to myself”), but also reveals that he pitched Johnson on his own backstory for what might break Luke and force him into self-imposed exile. Which is so insanely, comically dark that we’re just going to go ahead and quote Hamill’s own description here at length: