While I don't know the answer, I'd think maintainability is the big constraint there. In the extreme case, imagine the difficulty of pinpointing and fixing any

While I don't know the answer, I'd think maintainability is the big constraint there. In the extreme case, imagine the difficulty of pinpointing and fixing any problem when all your systems are nested shells with a massive surface area. You'd need to take half the station apart any time something went wrong.