For a while there, Activision was releasing a number of licensed titles in addition to its major AAA releases like Call of Duty and Destiny. It seems those licenses have reached an end date though, as a few licensed Activision titles have been delisted from Steam, the Xbox Store, and the PlayStation Store.
Fans first noticed that The Amazing Spider-Man and The Amazing Spider-Man 2 were removed from stores. The games are adaptations of Sony Pictures' 2012 and 2014 reboot of the Spider-Man film franchise. Both games have been removed from all platforms, leaving Spider-Man fans to either track down the physical copies or wait for Insomniac's upcoming PlayStation 4-exclusive Spider-Man title.
This news was followed-up with the removal of Teenage Mutant Ninja Turtles: Mutants in Manhattan, a Platinum Games-developed brawler that was released only eight months ago. It seems odd that Activision would have a license for under a year, making it possible that Mutants in Manhattan was rushed simply to capitalize on a license before it expired.
This isn't the first time this has happened to Activision. Deadpool, developed by High Moon Studios, was pulled from Steam and other digital stores in December of 2013, only a few months after its June 2013 release. It was joined by X-Men: Destiny, Spider-Man: Edge of Time, Spider-Man: Shattered Dimensions, and X-Men Origins: Wolverine. Capcom's Ultimate Marvel vs Capcom 3 was pulled at the same time.
Activision still retains a few licensed games, including Transformers: Devastation, Transformers: Fall of Cybertron, Transformers: War for Cybertron, and The Legend of Korra.