There are also IP theft issues, and (while this doesn't apply to Apple) the burden of having to set up join ventures in China in partnership with a local firm where the foreign company has less than 50% ownership of said joint venture.
In such a "partnership" (if you can really call it that), there is a constant struggle between the Chinese and the non-Chinese owners of the venture where the Chinese counterpart is trying to absorb knowhow as fast as possible while the foreign firm tries to maintain their technological leadership over their partner so that they don't get marginalized. Perhaps the benefit of such a contentious relationship has been eroded enough from higher wages and other costs that firms have started to migrate their operations back home.
In such a "partnership" (if you can really call it that), there is a constant struggle between the Chinese and the non-Chinese owners of the venture where the Chinese counterpart is trying to absorb knowhow as fast as possible while the foreign firm tries to maintain their technological leadership over their partner so that they don't get marginalized. Perhaps the benefit of such a contentious relationship has been eroded enough from higher wages and other costs that firms have started to migrate their operations back home.