Former Nintendo of America employee Kit Ellis has revealed in a new video that The Legend of Zelda: Tears of the Kingdom had the tightest security of any game he had been involved in with the company. Ellis says that less than ten people at Nintendo of America had the disclosure level required to even know about it before the game’s reveal at E3 2019. m
Kit Ellis: Zelda Tears of Kingdom reveal had higher security than any game he was involved in

I mean this was the most anticipated game back in 2019, it makes sense why no one knew about it beforehand.
The security was more than likely tighter than fort Knox.