Would they?
Foxconn for example pays a lot more than other companies in the area. There are plenty of people everywhere in the world who love to get paid overtime work. (Yes, Foxconn pays for overtime). They provide very cheap accommodation and food, so workers don't need to travel to work, they save most of their wages, and after two or three years they return home as rich people.
Someone working at McDonalds in the USA may have a higher income in dollars, but that person also has hugely higher living costs and probably can't manage to make any savings.
Now look at the software industry in the USA, where people are working 80 hour weeks (which is BTW. completely idiotic and their managers should be flogged and fired for stupidity). Or what happens if you want to become an MD; the same kind of extreme working hours. Any strikes? Anyone on the streets? No.
But what you haven't said: What working conditions are you exactly complaining about? Except for comparing it to slavery, and saying how awful it is, you haven't actually said _what_ you think is happening that would be awful.
Workers in China are not represented by any Union.
They can not strike and/or demonstrate in public.
They keep their workplace because behind them there is a queue of 1000+ ready to take their job. Poverty issues.
They hardly have any medical assistance.
Suicide rate is still very high.
They don't go back home as rich men/women, most of the money they earn they send it to their relatives at home.
China is not a democratic country, is still a dictatorship, the outside world knows only what they want to be known. Apple included.