I really don't see why Nintendo didn't produce a bit more on launch - I mean, they're not some kickstarter newbie - don't they have some skills in demand-forecasting?
Not to mention that having the production capacity to meet initial demand on a popular product would be an huge waste of money.
Best case scenario, a week or two after launch, the vast majority of that capacity would be sitting idle after the initial rush is over and the purchase rate tapers off. Worst case scenario, the product isn't as popular as you anticipated and you've got a big ol' writedown to deal with. (Atari anyone? Blackberry tablet?)
It spikes demand. Crazy parents run all over the place looking for it.
The winners are Nintendo, who gets sales in the 1Q, which is normally death for this kind of product, and the retailers, who get parents visiting daily and buying other crap.
My brother spent weeks looking for the "cream pie in the face game" last year. In the process, he picked up a half dozen other board games.
They have slow production on purpose. If you could walk into any store and get one, it wouldn't be nearly as big a deal.