It may sound odd, but this is standard practice in most "recycling" environments. When you recycle an aluminium can it doesn't get refilled. It gets melted into new aluminium. Even if the can is perfectly good and could be sanitized, to ensure constant quality it is best to start anew from the fundamental ingredients. Seeing a macbook shredded looks horrible, but if those bits are being properly recycled into new components then I can see apple's point. Rebuilding from the ground up is probably much easier than picking and testing every little component to ensure quality.

If you own a car, it has steel parts. Some of that steel is recycled metal from old cars. We consider it new. But would you be willing to pay the same price for a car with a chassis harvested from an older car? What level of testing would be needed for you to pay the same price as the car with a chassis built anew? If that testing costs more than a couple hundred, the logical thing is to melt.