People in my group asked the same thing. I agree that the camera could be better (particularly indoors), but I think it's sort of weird to compare the interface to WoW, which is a first-person (or third-person over-the-shoulder, which is effectively the same thing as far as camera control goes) game. You might as well ask why the cameras in Titan Quest or Civ 4 don't work like WoW's.
Obsidian are mostly to blame for the confusion, I think. They went to a lot of effort to design a game engine that lets you zoom all the way in and tilt up to see to the horizon, like a WoW-style game. That was an unfortunate choice, because it doesn't really add anything useful to the game, and people are so used to playing WoW that they are going to latch on to anything that feels familiar. But NWN still controls, first and foremost, like a Diablo-style 3/4 overhead view game. It's best to just treat it that way, instead of trying to make it into a poor-man's WoW interface.