How do you know? Source please?
Apple will unveil the iPhone 7 tomorrow, and it will go on sale worldwide just one week later. Times have changed. Nintendo can easily do the same with NX.
Nintendo aren't Apple, they don't have Nintendo stores scattered around the world to make distribution easy.
They are coming off the Wii U so they are having to sell to retailers a product with a "new concept" that may not be successful.
This is not a mass market product like a Smartphone from Apple. It's a video game machine.
They need retailers to manage inventories and get pre-orders for the NX. Especially when Wii U failed hard, retailers aren't going to risk taking another bomb unless there's good word of mouth and the pre-order figures to prove it.
A 1 week announcement to launch isn't going to guarantee that. All you'll get is a Sega Saturn launch and a new dead console.