TL;DR: R-Type Dimensions III is switching from a Game Key Card release to having the full game on the card. Because of this, the physical release MSRP is increasing by €10. They will honor the old price for existing pre-orders.
Initially, the publisher said that this was made possible by the new smaller capacity cartridges that Nintendo just announced. Later, they updated the press release to remove any references to cheaper cartridges and instead said that Nintendo did not announce anything.
I do get that 64GB cards are much more expensive than key cards. I don’t get why they don’t offer other sizes.
They did not have other sizes at launch. If you read the article, the game publisher let slip that Nintendo has started offering smaller, cheaper carts.
My theory is that the Switch 2 launch was rushed. Nintendo had been delaying the system for years, saying that Switch 1 sales where still over performing expectations. Last year, Switch 1 sales fell faster than the Nintendo expected and suddenly they had a system ready to release in a couple months. I would have expected the pre-release hype cycle to be longer but I suspect Nintendo expected the death of the Switch 1 to be much slower.