Think about how it works.

Apple has to be ready with hundreds of thousands of the item ready for the release date, maybe a million or more. The production for that kind of thing is tightly scheduled. Both for the logistics of the materials that have to come together, and for the economics of same.

Apple has fronted serious cash to have that quantity of items ready for sale. They need to be sold to recoup.

Depending, it might be the lesser hit to sell old stock at a discount, than to suffer the costs of holding back a product that is ready to sell.