Its the same reason the Avengers game has character models that are just slightly off the movie models: they want to have the lowest barrier of entry possible to existing fans without having to give credit or money to the success that they're trying to ride.Yeah, it has been confirmed that this game is not connected to the Arkham games, and is something completely new.
Arkham Knight spoilers:
It just seems so strange, then, that this game's version of Batman seemingly dies the exact same way that Arkham series' Batman died(?).
Surely there are lots of different ways to have Batman killed off, and having him explode in his mansion, seemingly by his own doing, is an oddly specific way to do it, if this isn't supposed to be connected at all.
Im not suggesting that there is some kind of conspiracy here - if they aren't connected, then that is fine - it just seems weird to me.
Marketing, everybody!