I guess they are more clever in gaming the system than you. US children can sponsor their immigrant parents. If they have aging parents, what better way to care for them than US Social Security, since social security pays anyone legally here over 65 with a low income. If the family members are disabled, including mentally, they can collect SSI.
It seems the Chinese govt. knows about this and encourages this to lessen their cost and responsibility for their own elderly.
People would've revolted long ago if they knew half of whats going on.