First it is not easy to get your money out of china for most citizens, so this is seen as the only investment they can trust and control (you really think you can trust Wall Street, china’s version is much much more corrupt).
Second they have 2 or so billion people over there most of which live in the poor countryside and must move to the cities to survive.
Third they must find about 25 million new jobs every year to keep the masses form revolt (there are riots in china everyday no one in the outside world ever hears about, if we could find 3 million new jobs it would be 2005 all over again to put it into perspective).
Fourth and yet they cannot continue this pace forever.