Game-key cards are different from regular game cards, because they don’t contain the full game data. Instead, the game-key card is your “key” to downloading the full game to your system via the internet.
Pay a premium for a physical copy of your game, and the cartridge may not contain the actual game. Only on Nintendo Switch 2.
One thing I don’t see people mentioning is that Nintendo Switch 1 game cartridges had 32gb of storage. We don’t know about regular Switch 2 cartridge storages, but they’ve already announced games like Elden Ring and Hogwarts Legacy that are much bigger than that. Add in the fact that Switch 2 promises games in 4k (when docked) and there’s a very decent chance that these game-key cartridges exist because some games wouldn’t fit in cartridges and would otherwise have to be digital-only or not be on this console at all.
I don’t think there is anything stopping nintendo from making 64GB or larger cartridges except the cost.