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.
Nothing new here. PS3 games were famous for requiring an install from the optical media to the internal drive first, and then also downloading some mandatory major update before running. The role of the physical media was mostly symbolic.