10. Alien 5
The Movie: In early 2015, it was confirmed that District 9 director Neill Blomkamp would be directing a fifth Alien movie, which would effectively disregard Alien 3 and Resurrection, instead acting as a direct sequel to Aliens, where Hicks and Newt in fact survived.
Why It Got Cancelled: Ridley Scott is largely blamed with torpedoing the production, pushing ahead with Alien: Covenant instead, causing Blomkamp to move onto other projects.
Scott officially confirmed that Alien 5 was cancelled this past May, and its original title, Alien: Awakening, was instead going to be used for the next movie in the Prometheus trilogy, to rub salt in the wound.
Though it's easy to rag on Scott for his rather tactless derailment of Blomkamp's film, it's ultimately probably for the best, considering Blomkamp's post-District 9 track record, and the fact that decades-later sequels very rarely work, even with extremely talented directors at the helm.
Scott probably did fans a favour in the long run, even if he's hardly putting out classic Alien movies himself at the moment.