Like you said, they are separate games with separate developers.

A lot of restrictions and constraints that the main game has are imagined. Like how Luke thinks using the force is impossible in Star Wars ESB. I believe they wouldn't even deny that some of the restrictions are due to arbitrary, self-imposed polygon limits they have to prevent a 1.0 situation where some things were high quality, and some were low quality, leading to a mismatch when you walked around and saw the world as a whole.