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.
It’s not unheard of, though. Modern Warfare 2 had only a 70MB file on its disc, basically a license, and required you to download the actual game.
Note I’m not defending this. It’s a nightmare for game preservation and pushes us ever further in the direction of never owning anything. I’m just saying Nintendo isn’t breaking new ground with this particular outrage.