Because Chinese labor is a lot cheaper than maintenance on expensive assembly machines. Apple brings in up to $300 profit from each iPhone, but they rather put that money in their own pockets rather than to create jobs with a decent wage in the US or China.
It doesn't bother me that companies take jobs to China, what bothers me is why they do it. They do it to exploit them with bad wages and killer hours, not to give them jobs.
A reason why I will never again buy an iPhone/iPad/Mac
You're completely hilarious, and a troll. It's like saying you will never again buy a Ford car because they include a steering wheel, ignoring the fact that every car on the planet is similar. Please, enlighten us as to which consumer electronics companies you plan to support instead? I'm honestly curious, since Apple is the only that as actually put in alot of effrot into improving things and is seeing real, tangible results as evidences by the findings of the Fair Labour Association, which conducted an independant audit of Apple's suppliers (at Apple's request), something completely unprecedented for any electronics/computer company. My guess is you're simply an anti-Apple troll, like many others online, who couldn't give a shit about Chinese workers or labour, have never uttered a word against any other company that manufactures in China (which is all of them) but simply use the issue as another tool in their Anti-Apple bashing toolbox.
So again, be intellectually honest, and tell us from which company you now plan to buy your computers/phones/tablets. I've asked this of many people who have expressed the same thing as you online, and as of yet haven't gotten a single answer. And I don't expect to. It's evidence that their self-righteous bleeding hearts is a sham.