PS4 and Xbox One sold incredibly well at approx 2million units on launch. The Wii U sold under a million and sold out. PS4 and Xbox One were incredibly popular machines, however, the Wii U, whilst pulling a respectable number, had half the orders to fulfill. It's a trend that has continued first with the Amiibo's and then the NES classic with numbers being supplied far outstripping demand.
It's also worth nothing that the PS4 and Xbone were available shortly after it sold out and maintained high sales whilst the Wii U's sales stagnated, even during the holiday period. The Wii was massively successful but had stock issues for years and given how cheap the thing was to manufacture the only rational behind it was to keep the 'hot toy in town' narrative alive and since then they've done it with everything they've released. #
Sell out's happen on launch but there are countless articles about Nintendo understocking there products to create demand