some programmer somewhere arbitrarily chose a number that they felt sounded reasonable
probably easier to fit the names in the ui and speech bubbles
That’s a great point. Especially with fonts that aren’t fixed-width.
They probably take the widest character (like a W or something) and say “a user’s profile name can be at most WWWWWWWWWW in width”.
It’s very possible an intern just thought to himself “what’s a good number for the maximum length of a username? I know. 10.”
You can’t just not have a length limit. Don’t want people literally putting whole novels in the username field.
They’re more often limited to 16 characters than any other number so I assume it has something to do with how they are storing it in memory because it’s a multiple of 4.
Probably the same reason for only 10 characters, too, but it’s not as obvious.
I doubt there’s any technical reason for it, especially given that you can change your username at any time and other online services allow for longer usernames. I guess Nintendo just think that 10 characters is a reasonable cap for usernames.