Priorities. For Nintendo, size matters.
Time also matters. In an old interview, Someone from Nintendo says that the time to put the disc in the Wii and be able to play Zelda needs to be less than 30sec.
Nintendo save: bit-optimised tightly packed binary
NBA savegame: json encoded in xml, run through a base64 because < in team names was breaking saves, all packed in YAML because the new summer intern couldn’t find a parser library for anything else
A great example is the size of Super Mario Odyssey being 5.7GB and a save file from NBA2k18 being 5GB. https://www.nintendolife.com/news/2017/09/super_mario_odysse...