Nintendo policy reportedly prevents Switch 2 game-key card to be reprinted as full cartridge version
(nintendoeverything.com)
I have to imagine it's to prevent consumer confusion. To the average consumer the two look the same, and it could be confusing if a shop is selling "Game [Physical]" and "Game [Game-Key Card]" (and "Game [Digital]"). Nintendo just wants Physical and Digital.
That being said it's a policy and one that I think they should change. Or better yet sunset Game-Key card, and just have physical or digital.