Oye. There is so much bad information in this thread.
Lets step back - cartridges, as many are describing in this thread, dont exist anymore. Talking about the "no loading, fast access, expensive" storage mediums people keep bringing up. They work by physically addressing a eeprom, meaning tou have direct lines running from the console to every bit of digital (not analog) information on the cartridge. If I want to access, say, level 2 in mario, I point to address 0xblahblahblah and directly read it off the cart. The reason access is so fast, is because the area I am accessing is always addressed physically.
This is not how cd roms work. The reason cd roms are slow is because they are not directly addressed. Rather, you need to optically read data off the disc into a region of directly addressed physical memory called a cache to access it. The size of this cache is way, way smaller than the total size of the disc, and thus you must access all data in chunks. The time to read this data into cache is called loading time.
The way flash cards work - and ds games, and 3ds games, and assuredly switch games - is just like a cd rom. They have a small amount of cache on the card that is directly addressed that have lines running to a larger storage of flash memory that is accessed in chunks. To access the entire card, you need to load and unload in chunks, just like on a cdrom.
These do not mean "no loading."