Bofferbrauer on 03 January 2015
It's probably due to the convoluted design of the Nintendo development divisions (which are subfractioned even further) and the fact that Nintendo has studios specially for things like sound design, User Interface and engines, which all contribute to all their projects, meaning it's never just one single studio who works on a game at Nintendo.
Just to give you a quick overview: http://en.wikipedia.org/wiki/List_of_Nintendo_development_teams
