The Amazing Spiderman 3
Its because Spiderman 2 fell short on expectations.
Bill Murray never really wanted to do a third one and so many ideas were thrown around that they never got to do Ghostbusters 3.
The Girl Who Played With Fire
The director David Fincher just could never get to do the other two characters he was planning to do but production was delayed because of script issues.
Who Discovered Roger Rabbit
Who Framed Roger Rabbit was one of the biggest hits of 1988 so they wanted to do a sequel after doing test footage it was deemed too hard to make so it was canceled, but Roger Rabbit creator Gary K Wolf is still interested in doing a sequel but most likely won't be able to do it.
The Last Airbender 2
While The Last Airbender was a box office success it received so many people angered because it wasn't a good movie of Avatar The Last Airbender the show and is deemed by critics and audiences as the worst movie ever.
Fantastic Four 2
This movie fall short on expectations and was canceled.