Assassin's Creed failed after the death of Desmond. Sure, pretty much everybody loved A.C. Black Flag IV but the Desmond/Minerva tale ended at A.C. III and one of the original developers, years later, said that they had intended the final of the series to be A.C. III. Execs in several interviews for years said "We know where this is going. We know where the story will continue" but they were just trying to milk it for all it's worth. The final battle of Minerva took place in a freaking comic book of all things - A.C. Uprising.