"but I would think that the scope of any AAA game would be such that assets and code were kept separate." Sure, they are. In different files at a minimum, and

"but I would think that the scope of any AAA game would be such that assets and code were kept separate." Sure, they are. In different files at a minimum, and likely within a separate directory tree in the overall project. But not in a separate repository entirely! Look at how the overall software industry is going towards monorepos. Not just (or even primarily) games, but software in general.