Keanu Reeves – Speed 2: Cruise Control
Reeves wasn’t into the script so his character and Sandra Bullock’s broke up off screen and he was replaced with Jason Patric.
Crispin Glover – Back to the Future Part II
Glover didn’t agree to return because of some apparent “moral” objections. Instead, the production hired an actor to impersonate him and put him in prosthetics. That, combined with some footage from the first film, made it seem like Glover had reprised his role of George McFly. He was not psyched about this development.
Robert Duvall – The Godfather Part III
Duvall wanted more money so a new character played by George Hamilton was brought in.
Linda Hamilton – Terminator 3
Hamilton had issues with the script for T3 so her character was said to have died from leukemia before the film. She did return for Terminator: Dark Fate, which takes place between the second and third film.
Jamie Lee Curtis – Halloween 4
Curtis had moved on from her scream queen days by the time this installment rolled around so the story shifted to focus on her character’s daughter being terrorized by the same sadistic lunatic.
John Cusack – Hot Tub Time Machine 2
Money issues forced Cusack out and Adam Scott was brought in as his character’s son. Great Scott!
Marlon Brando – The Godfather Part II
No one is exactly sure why Brando didn’t return for a cameo, so his character is kept offscreen while the rest of the family discusses Michael joining the Army.
Natalie Portman – Thor: Ragnorak
Portman was reportedly upset with Marvel’s decision to hire Alan Taylor over Patty Jenkins for Thor: The Dark World and declined a role in its follow up. Thor mentions that HE broke up with her – and not the other way around – in the third film but Portman will return with her own hammer in the upcoming Thor: Love and Thunder.
Will Smith – Independence Day: Resurgence
Smith opted to star in Suicide Squad instead, which was filming at the same time. His character was killed offscreen while testing a new alien hybrid fighter.
Sean Connery – Indiana Jones and the Kingdom of the Crystal Skull
Connery didn’t think the part had enough meat to it so he passed and his character died before the film began. Good call, stay far, far away from Mutt.
Megan Fox – Transformers: Revenge of the Fallen
Fox had a pretty public feud with Michael Bay so it wasn’t a surprise that her character was dumped by Shia LeBouf’s character in-between films.
Richard Dreyfuss – Jaws 2
“No Spielberg, No dice”, is what Dreyfuss said, I’m guessing. While his character Hooper speaks over the phone to Roy Scheider’s Brody, he is said to be on expedition in Antarctica.