Saves being on the Switch only is probably an anti-piracy measure. Thats my guess at least. Same reason why they dont have a browser. Same reason why Sony bundled the game and save together on Vita, so that people couldnt mess around with save game exploits.
People really need to stop thinking that Nintendo has some master plan rationale for missing out on obvious features or understanding the needs of their customers. Because more often than not, it's not an intentional omission, it's just a stupid decision due to inexperience handling the concept of service driven products.