Miyamotoo on 30 October 2016
Isn't that very obvious!?
1st they said several time they want much less time between reveal and actually launche and if they reveal Switch too early competition could have still their idea.
Also revealing new platform on E3 isnt good move, because you are not only news and you basically need to fight with other news on E3.
Sony and MS didnt reveal PS4 and XB1 on E3 also, they revealed them on their own conference. Nintendo is doing own Switch conference in January.
