Most of the time when you submit paperwork for someone that is applying for a VISA here you'll provide information from a citizen/permanent resident, so they likely want to find the person that helped/sponsored your paperwork so they can get to you. Might be a good way to find bogus Medicaid fraud and strip you from your permanent residency or citizenship or just say you're abetting a criminal (someone living here illegaly), there are plenty of uses for this data if you're evil enough.