If they opted for another option, one of two things would happen. The Switch would be a dedicated home console, or the price would go up. With the former, that implies HDD usage. Which, a mechanical drive on the move is prone to damage. The latter implies a SSD or higher storage capacity. That or higher cost for games, with a larger cartridge storage. They COULD have gone disc for cheaper but larger capacities, but that's an issue in and of itself. Would probably leave it as a home console as well.
Using MicroSDs is as good as we'll get for now. That's perfectly fine. You pay for the storage you'll actually use. Some don't even fill the PS4 or Xbox One.. Crazy right? Given average game sizes...