The reasons people are leaving are wide and varied. There seems to be 3 core reasons 1) Salary 2) Lifestyle/rostering 3) Pollution.
Each will use one, or all of the above depending on how they feel on the day. For example, one poor chappy cited pay as the main reason for going back to Oz, but then decided that it was actually for the sake of his childrens health. I'm not saying for a minute that your families health is not important, but I think some get a bit confused with the exact reason for them leaving. The same guy said he'd probably stay if they gave us all A scale! In fact, many have said the same thing, going as far as saying that they would do anything that the company asked them!
The same guy above has hated HKG from day one, but thought it was ok to keep his family here long enough to get his gratuity! All for your families health? Yeah right...