User blog comment:Master Sima Yi/Assassinews 14-07-'14 – Two new Assassin's Creed: Unity trailers/@comment-24760042-20140801200335/@comment-1153722-20140805084248

Brotherhood was not meant to be DLC. Assassin's Creed III was originally going to end in 1503 (with Rodrigo's death) as can be heard in dev diaries for the game. However, during production the idea for multiplayer was conceived, and they decided to shorten the plot for Assassin's Creed III to have a backdrop for the singleplayer for Brotherhood. The third game was more of an experiment. Then the executives decided that these games make too much money to skip one year, and Lost Legacy was turned into Revelations. Circumstances led to Ezio having three games, not a pre-envisioned road map.

And Ubisoft is a big camp, with its own narrative team working on Assassin's Creed and a lot of different scriptwriters being hired. And thus, a lot of different ideas for characters. Travis Stout, the writer for Assassin's Creed: Unity, is newly-hired, hasn't worked on any of the previous games, so he'll be able to bring some fresh ideas to the table. Also bear in mind that the protagonist is not the only character that needs creating. Each new game has its own batch of new characters.