My thoughts are that the small cartridge is relative to an SD card, or a USB flash drive. The reasons other companies don't use them is because they are expensive to use unlike discs. The speed of the cartridges are faster than discs as well.
Hopefully the cartridge usage in the Switch doesn't drive prices up too much because of it. I get that production is more expensive, but after a certain point there are definitely some questions about why standard flash storage solutions aren't good enough.