: I want to believe that the vast majority of people would be happy that it's
: there period, regardless of if they get to see how (I don't know the word
: to use here) things look behind the scenes with loading/rendering etc.

Game developers have an ego, much like anyone else. Bungie definitely put more effort into the skybox and out-of-bounds areas in Halo 3, ODST, and Reach so they wouldn't fall apart when viewed in theater, because even if there's people like me that go "neat, that's how they did that", there's many more people that go "olololol they just used a billboard sprite there, how lame".

For example, in Halo 2 they probably would have made the scarab actually fire it's cannon from over the tunnel, instead of using a floating plasma rifle. Stuff like that. Stuff that you usually do in your later iteration passes.

It probably wasn't the only reason, but it definitely had to play a part.