mxu12, You don't sound like a dumb person, why is it so hard for you to enlist some reasons yourself? OK let me give you a few: (not necessarily the reasons for me to stay here)
(1) Like USA's peaceful life and clean environment (but they don't have to hate China like you do.)
(2) Already get used to the life style here, too hard to change when they are not young anymore
(2) Kids were born here and are in schools, because of the language and culture differences, it is even harder for kids to move back to China, so parents can not move until kids are independent
(3) Have a comfortable job or business here with decent income, but their skills are useless in China.
(4) Many more...