Developing a video game is a difficult and long process. There's no guarantee that the final product will be successful. It's even possible that a project won't be completed. Companies go bankrupt, designers come and go, games can end up in a developement hell and it's possible that a game may not see nor reach the light at the end of the tunnel. Canceled games happened even in the DOS era.
Some of the most popular abandoned "canceled game" games: