For the same reason they use Seagate and Sony (batteries) and products from other manufacturers: they are all in the business of making and selling the parts for others as well as their own computers.
This thread has been closed by the system or the community team.
You may vote for any posts you find helpful, or search the Community for additional answers.
TOSHIBA MK5055GSXF Media Disk in My Macbook Pro 15 i7, Did I buy a fake?
Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.