Hahaha I have asked this question myself.  And people don't just leave, they pay a pile of money to leave if that's what it takes and they are able to.  Often it's the really well educated people leaving, and you'd think that they would be the ones who would enjoy the best life that China has to offer.  Doctors quit their jobs and leave China to deal blackjack in a Canadian casino.

One reason other than the obvious reason is that they might be able to make more money in the long run in another country to send back to their families, and they might plan to retire earlier and go home where the cost of living is lower.

  Who said it was so great? Rats, bad water, lack of personal freedom to live and say as you please, I don't see what's so great about that. People go where they can afford to go. If I was loaded i'd try and start a life in Sydney, or maybe back home but down south, in Cornwall. I'm only here because it's a more desireable option than the economic slavery I was subject to back home. I mean, who wants to work in warehouses twelve hours a day for the rest of their life just so they can keep a roof over their head? Not me.