I'm not sure I understand what you are proposing. Apple should... make demands on companies with which it has no relationship, and expect those companies to comply?

As I stated, Apple did insist on improved conditions at the Foxconn factories where Apple products were made. They audit the factories regularly to ensure Foxconn and other contractors are meetings the standards Apple has set for employee treatment, and report on this information annually, including dropping suppliers who fail audits.

It is not clear Apple could do more than they're doing, other than raising the standards even more. Which... maybe they should, but I don't think that's even what you're suggesting.