Mibu no ookami
Member
Their current cartridges are reportedly quite expensive to produce, which is why you basically never see the 64 GB carts used and very rarely see the 32GB ones, so you could still see a storage solution that is larger *and* cheaper than the current carts while still being markedly more expensive than bluray discs.
Also, if you, as a consumer, are paying $10 on average for a 128 GB micro SD card, manufacturers are paying way, way less, so there's no reason to believe Nintendo would be paying anywhere close to $10/cart when they're producing tens of millions of them.
Manufacturers aren't paying way less. I think there is this world where people think companies get this MASSIVE bulk discount on things like this, but there comes a time where you have minimal margins in the first place.
No matter how many carts they produce it won't be nearly as many as SD Cards have been produced. Their cards are marketedly more expensive than SD Cards. They use a proprietary card to limit piracy, but it comes at a higher cost.