You forget the wiiu had the option of a 1tb external hdd
You have a fundamental misunderstanding of how emunand in general works
Edit: Just so we're clear what I'm talking about and it doesn't just sound like I'm being an asshole (because I'm not trying to be), emunand (or any drive that's being cloned, for that matter) needs exactly as many bits OR MORE as is on the partition being copied for the new drive to not be reduced to a corrupted mess. Since Nintendo consoles have historically kept both the system and data on the same chip, but keys on a separate, very small one on the SoC for security, that means we need exactly as much as is advertised on the console box... Plus a little bit extra, which unfortunately means you need to go one size up since flash memory is only sold in powers of 8.
The reason that hasn't been an issue until now is that up until the Wii U, Nintendo never had a console with any significant amount of storage. The Wii only had 512mb, which doubled means a 1GB SD card requirement. 3DS had 2(?)GB onboard, which meant a 4GB SD card. The Wii U had an 8GB version that could skate by with a 16GB emunand, but unfortunately the "Deluxe" version required a 64GB card; as will the Switch, most likely
Also, due to some techno-bullshit I don't understand, emunand almost always has to be on an SD card, rather than a hard drive. It probably has to do with the SD bus being the same as onboard storage (since they're both flash memory) or something like that