Those requirements can be anything from a powerful propulsion plant, mini hotel rooms to aesthetics. Everything else is then second (or third etc) to that. So yes, something could logically be built as a shell and filled with systems. Its just that most things arent made to look pretty but to do a job.
If the requirements are a Zeppelin-shape for aerodynamics and most-volume-per-area fuel tanks, you have plenty of space.
Luxury ships often scarify 10..50%, of their maximum efficiency for comfort or even a thicker hull if the owner wants to be proud about it or is paranoid enough.
Big American cars for a single person with 12 litre per 100km (18 per 100 miles?) are a very good example for building around (or inside) aesthetics.
The problem is that not all peoples are ready to pay the price of freedom.
((and that few peoples on top reserve the money required for that freedom for themselves through taxes or running license costs))
And not even RL military ships have as few interior as some SM ships. It wouldn't be possible to exchange broken parts without accounting for that.