There’s a specific reason why Skull & Bones isn’t an Assassin’s Creed game, and the game’s creative director, Justin Farren, has come forward to explain why.
In an interview with GameSpot, Farren said the team over at Ubisoft Singapore did not want to make a game "about being an assassin, about being in a crowd," but instead wanted focus "on the details and intricacies of the ship" and bringing "the ship to life and make it a character of its own."
However, Ubisoft Singapore did take plenty of inspiration from Assassin’s Creed IV: Black Flag’s naval gameplay, specifically the way people responded to their ship in that game, the Jackdaw. The studio wants "people to really develop a relationship" with their ship in Skull & Bones, just like with the Jackdaw, "and invest in its customization and everything that comes with it."
Source: IGN PC Articles