We have many credibly reports that slaves have been placed in concentration camps virtually entirely because of their ethnicity and or religion where they are obliged to work for free. The malfeasance of China in this regard and others for example using religious minorities as literal organ banks to be slaughtered for parts has been discussed for years. Anyone who claims at this point to be "investigating" is entirely dishonest. Characterizing this as one report is entirely incorrect.
They haven't changed because moving away from china would cost them billions and they as most people would rather keep themselves warm with a pile of money than worry about the ethical implications.
Nobody here is disputing that China is abusing Uigher people.
But now you've shifted from the part I found dubious--that companies are knowingly engaging in slave labor--to a more clearly established pattern. One can be both horrified by China's treatment of Uigher people and skeptical that Foxconn, Apple, or any one of the 82 companies to which you've referred are complicit.
They haven't changed because moving away from china would cost them billions and they as most people would rather keep themselves warm with a pile of money than worry about the ethical implications.