Nintendo has to be eating a good chunk of the cost per cart because CD Projekt wouldn't be that nice to them.
Prices of Memory, including flash memory, are crashing down. I'm pretty sure a 32GB cartridge these days is cheaper to produce than a 16GB cartridge was during launch of the Switch.
For instance, you can get 256GB MicroSDXC for 30€ now. Just half a year ago, you would have payed 50€+ for that. 32GB MicroSDHC for less than 4€ now, 2 years ago, 16GB would still have been over 5€.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454