Update thanks to thethatfox:
Physical game cards may also not actually contain the game:
Nintendo Switch 2 Game-Key Card Overview
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.
Update 2: There is probably a difference in Game-key cards and card that contain real game data. So we don't know right now how often these game-key cards are used or if nintendo is using them.
I hope this is only for certain games and they specify it on the box (like those scammy boxes they sell you like physical games, but that say "digital download code included" and there's no cart), because otherwise it's a complete scam. Imagine you're on a trip and buy a Nintendo Switch 2 game in a shop and can't play it because your Switch 2 isn't connected to the Internet. Or they close the shop and your memory dies and you can't download that game you bought for USD 70. This is really bad...
It's probably not for every game, we don't know that exactly right now. See this screenshot.