Just because a game can exist doesn't mean it should.
Bioshock was not a game that needed a sequel. It told a story and concluded it nicely. It didn't leave the door open for a future tale – this was made all the more apparent when the second game didn't bother to continue from the events of the first. Instead, it creates a whole new cast of characters and retcons the antagonist of the story into the events of the first game. The poor, hackneyed story is only the start of the problems with Bioshock 2.