1) the first obvious reason, Vorador is still alive
2) the second obvious reason, Janos is also still alive
3) the sudden introduction of the Hylden, who was never mentioned before, but only vaguely described in SR2, and also the very last minute
4) the REALLY awkward attemp to establish the continuity going from BO, BO2, and SR1
5) what seems like just sheer negligence of anything that is monumental in Nosgoth were hardly ever bought up BO2, certainly, no pillars scene, swamp scene, etc were included into the game
6) lastly, although the Iron armor were included in the game, it can never be obtained by normal game play. which could be considered as no connections at all to the other games
so really, it just seemed like the BO2 game crew made the game just so it can stand out by itself, but meanwhile have really created so many messy elements into the whole scheme, and the worst thing is, it really looks like they are counting on the SR game crew to clean up the mess by tying up loose ends in SR3 and beyond.

