Big shoe brand companies do not utilize a single factory to produce their shoes. They set a number of shoes per factory say 30,000, so the factory will not produce only 30’000 shoes infact the factory would produce extra pair of shoes say 20,000. This is because the brands do quality testing and if some shoes fail to pass the test, the factory would be responsible and hence the factory produces more sneakers if some sneakers fail to pass the test the extra sneakers will be sent to stores.

If however most shoes pass the test, there will a lot of extra pairs left, these shoes are not sent to the retail stores (just to increase prices and hype) and hence they got left behind.