Probably because Apple has one of the most generous return/replacement/repair policies in existence. Fortunately they build that cost into the price of their products, and then get a bit more in some cases with Applecare.
Much morso than almost any other vendor, they will replace a unit that is having a problem. This means they end up with a lot of units that just need some basic work and then can be resold as refurbished.
Much morso than almost any other vendor, they will replace a unit that is having a problem. This means they end up with a lot of units that just need some basic work and then can be resold as refurbished.