Note: Please do not add "Joel Schumacher died in June 2020" reason, because this was before that happened.
Robin was a spin-off film to Batman and Robin, but was cancelled due to the critical and box office failure of the film. Actor Chris O'Donnell, who played Robin in Batman Forever and Batman and Robin, revealed in a 2012 interview with Access Hollywood that there were plans to develop a Robin spin-off film with him reprising the role. 
The plot is for the most part unknown. It would likely focus on how Robin became Batman's sidekick.
Why It Was Cancelled
- Batman and Robin flopped at the box office and received extremely negative reception from critics, audiences and fans of Batman (mentioned earlier).
- Joel Schumacher admitted that both the spin-off and other planned films in the franchise should have been the studio's next step instead of producing Batman and Robin.
- Joel Schumacher decided to step down from directing all future Batman films.
- Robin was permanently cancelled.