If you have poor internet, then you may prefer physical cartridges, to avoid needing to download large files.
If you are like my parents, you might not trust the internet for purchases and only buy things in physical stores - so the physical copy is better.
If you are paranoid, you might not trust Nintendo to protect your account from hackers, who might mess with your digital purchase history. And one day will Nintendo closes it's digital store, and downloads will not be possible (has happened for DS). For both these reasons you might get the physical copy as a guarantee that you will always have access to the game you paid for.
You may have friends. In this case, a physical cartridge will let you lend games you've finished to your friends. Hopefully they'll let you borrow some that they've finished.
Otherwise, yes, the convenience of digital makes that purchase method better for most people.
(edited to include suggestions from comments below)