In terms of gameplay mechanics, old school zoom aiming achieves the same thing as ADS. Is getting to press your nose against virtual firearms really that important in a game about shooting werevolves and vampires?
I blame this on the proliferation of Call of Duty over traditional scifi and fantasy shooter franchises. You can fucking ADS on an assault rifle in Halo now 
I just don't see why it's necessary to scope even with guns like SMGs. In a game like COD where you can die from a quick burst it makes more sense, I guess, but Halo was more about strafing and peppering your enemy with hipfire rather than quick potshots
spoiler
Though in actuality it was about tossing your SMG or AR in the trash and picking up a precision rifle at the earliest opportunity, at least in multiplayer