Editor's note: Because I am an idiot, I didn't realize this came from the same source as the Wii source code leak. I earlier mentioned that I would not be sharing info from that particular leak, yet I goofed here. Going forward, we will be extra sure to make sure we do not share content coming from that source code leak. Any stories we have about the leak will be tied to the leak itself, not specific details on what was found in the leak, including source code, game assets, and so on.
A document has surfaced that is basically a presentation on Nintendo's idea to use Friend Codes on the Wii when it came to online play. A lot of people wondered why Nintendo went with this over traditional usernames, and thanks to this document, we fianlly have some clear-cut reasoning.
With the Wii, Nintendo was worried that people who signed up with screen names would become frustrated when they saw that the name they wanted was taken. This might result in people trying multiple names, only to find them all already registered. Nintendo was worried this frustration would take away from the Wii's aim to be a simple, easy-to-work-with system.
Nintendo was also worried that people might be able to guess the screen names of other people just by trying different combinations of names. In Nintendo's opinion, this might make some users uncomfortable, as their names could be sought out and contact could be made by strangers.
Why did Nintendo move to screen names with the Wii U, and then back to Friend Codes on Switch? Your guess is as good as ours, as the document only covers the original decision for the Wii. It's fair to say the Wii and Switch share a lot of similarities in approach to the gaming audience and ease of use, so perhaps that's why Nintendo adopted their old idea once again.