Ahsoka is a rather important character in Star Wars, as her character arc expands over all three eras to an extent. With the release of Season 7 of The Clone Wars, Ashoka would have been the perfect addition to Battlefront II because she is already on the minds of the fans of the show.
It's no secret that Ahsoka Tano is a huge part of the Star Wars franchise, so why wasn't she a part of Star Wars Battlefront II?