Another article with more details.
theweek.com
Notice two things to watch from article, first is "india's sketchy infrastructure always held it back, but it has improved", and second is "Apple may be diversifying its supply chain, but other firms, such as Starbucks, are "increasing exposure." Politicians hoping to replicate China's supply chain ought to remember it "started building out the logistical infrastructure in the 1980s." It has taught "hundreds of millions of blue-collar workers to be seasoned manufacturing hands in sophisticated production systems." Replicating that elsewhere requires more than wishful thinking.
So as much as businesses want to diversify their supply chain from China, building out the logistical infrastructure to produce such large quantities along with meeting Apple's quality testing takes a long time to setup it up correctly in other locations. You might remember several MacRumors articles concerning the example of a Chinese display company getting rejected by Apple for several years, then finally performing to Apple's quality specifications.

Troubled union: Apple's China problem
How will Apple branch away from building products in China?
Notice two things to watch from article, first is "india's sketchy infrastructure always held it back, but it has improved", and second is "Apple may be diversifying its supply chain, but other firms, such as Starbucks, are "increasing exposure." Politicians hoping to replicate China's supply chain ought to remember it "started building out the logistical infrastructure in the 1980s." It has taught "hundreds of millions of blue-collar workers to be seasoned manufacturing hands in sophisticated production systems." Replicating that elsewhere requires more than wishful thinking.
So as much as businesses want to diversify their supply chain from China, building out the logistical infrastructure to produce such large quantities along with meeting Apple's quality testing takes a long time to setup it up correctly in other locations. You might remember several MacRumors articles concerning the example of a Chinese display company getting rejected by Apple for several years, then finally performing to Apple's quality specifications.