They claim there’s a technical reason instead of a financial one:
"Snowdrop relies heavily on disk streaming for its open world environments, and we found the Switch 2 cards simply didn’t give the performance we needed at the quality target we were going for. I don’t recall the cost of the cards ever entering the discussion - probably because it was moot.
“I think if we’d designed a game for Switch 2 from the ground up it might have been different. As it was, we’d build a game around the SSDs of the initial target platforms, and then the Switch 2 came along a while later. In this case I think our leadership made the right call.”
No explanation was given as to why they didn’t forgo the key card altogether and just release to the eshop only.
You can sell key cards. The software has to be downloaded, but it’s unplayable without the key card being inserted in the system. Without the key card, you cannot launch the game, but the card itself is not locked to your system. You can loan them or give them away, if you don’t mind losing access to the game the card is for.