I Wonder if Mark Hamill Refused to Return for Episode 9...
...and that's why they killed him so abruptly? It didn't really make much sense in the movie. We think he's going to die, then it turns out to be a trick and he survives, and we're like, yay, Luke is back, and then... he just randomly dies for no apparent reason. Um, bye Luke? Pretty pathetic sendoff for such an iconic character.
It would have made better dramatic sense for Luke to survive and be around for the start of the next movie so he could have a few more scenes and a proper sendoff. (They're going to have enough trouble filling out the runtime already!) I wonder if MH just refused to come back after seeing their treatment of Luke and they were forced to kill him off hastily.