Don't forget that NWN1's a big jump from BG1 in terms of design and interface (despite the lacking in plot for OC). Back then, 3D graphics hasn't really been part of the RPG world so it is understandable that NWN has a long development time. NWN2, on the other hand, borrows much from NWN1 which is why it has a shorter development time.
I think BG's interface is much better than NWN1's, just on account of the radial menus.