There are several reasons why sequels fail. First of all, some of them did not reach movie quality (Speed 2, Highlander II, Rocky V, etc.), some had disappointing cast and crew changes (Son of the Mask, Grease 2, Hannibal), some were too long overdue and people did not want them ( The Rage: Carrie 2, Blues Brothers 2000, The Odd Couple II), and those that failed to exceed expectations due to the sheer popularity of their predecessors (Alien 3, Cristal Skull, Batman Forever).
These films have not performed as well as expected, but they have taken their places, winning Razzie Awards and becoming cult films.
