According to an article in the NYTimes [nytimes.com], at a dinner in Silicon Valley last year Barack Obama interrupted Steve Jobs and asked:

Why can’t that work come home? Mr. Obama asked.

Mr. Jobs’s reply was unambiguous. “Those jobs aren’t coming back,”

A former Presidential adviser said this about Apple:

“Apple’s an example of why it’s so hard to create middle-class jobs in the U.S. now,” said Jared Bernstein, who until last year was an economic adviser to the White House.

“If it’s the pinnacle of capitalism, we should be worried.”

The reason is because they feel the scale of the work, the speed at which it can be done plus the lower cost means the work cannot be done in America. But the real reason is that the work can't be done under the horrific conditions Apple can get away with in other countries. Apple contracts nearly 700,000 people outside of America.

One former executive described how the company relied upon a Chinese factory to revamp iPhone manufacturing just weeks before the device was due on shelves...

A foreman immediately roused 8,000 workers inside the company’s dormitories, according to the executive. Each employee was given a biscuit and a cup of tea, guided to a workstation and within half an hour started a 12-hour shift fitting glass screens into beveled frames.

How much human suffering and exploitation is ok to make Apple products? The CEO of the Chinese company that makes Apple products regards his employees as animals: [businessinsider.com]

"Hon Hai has a workforce of over one million worldwide and as human beings are also animals, to manage one million animals gives me a headache," said Hon Hai chairman Terry Gou... adding that he wants to learn from Chin Shih-chien, director of Taipei Zoo, regarding how animals should be managed.

After Apple was shamed into looking at the labor practices and found instances of slave labor, child laborers and workers forced to work over 60 hours per week:

In the course of the 229 audits, Apple said it discovered several violations, including instances of underage labor at five facilities. Apple said it required the suppliers to support the young workers to return to school and to improve their management systems to add age-verification procedures. Apple also said it found instances of involuntary labor and stopped working with one of suppliers involved.

Apple also discovered at least 90 factories with records showing workers were exceeding its maximum of 60 hours a week and at least one day of rest per seven days of work. The company found violations of anti-discrimination rules for workers who were pregnant or had hepatitis B. Apple said it made the suppliers end the discriminatory screenings.