Traditionally, toy companies will have a "tent pole" item they hype up and sell out of before Christmas (originally Cabbage Patch Kids but later on Elmo, Wii, etc.) This forces parents to less desirable accessory products for Christmas. Mysteriously after Christmas the tent pole item is in stock.

Eric Clark's book "The Real Toy Story" goes into the origin of this and other trends [1]. Nobody is really wild about the idea, but the industry is kind of forced into it because sales are literally all within a 3 week period. Miss it and you're dead. Tactics like the 'high demand, low availability' hot Christmas toy are a matter of survival.

[1] https://www.amazon.com/Real-Toy-Story-Ruthless-Consumers/dp/...