Very light with hardly a flat slab to it (less than a square foot !) and excellent workmanship in building and finishing it.
Now compare that to your car.
Lots of flat slabs - often of the see-thru kind
Rubbers sticking out into the breeze to hold those windows.
Panel and door gaps.
Windshield wipers that for the most part aren't aerodynamically covered (despite that it has been known for years that they also cause additional injury to pedestrians when exposed).
Sharkfins that are mounted as standard even if none of the equipment that requires them is installed in the car.
Roofrails standard with free option to delete them - rather than the other way around.
Dirty underside, though all manufacturers know it'd improve the mileage to clean up that mess.
The list is nearly endless.
They all like to keep something behind the cupboard to make future improvements, rather than apply known mods NOW and research others for future use.
Maybe governments should force the simple measures that are known to improve mileage upon the manufacturers as must-do measures, rather than do-as-you-please.