I've wondered about it too, but I think it might just come down to it's far easier to say "papers, please" and verify them, versus auditing a business to unders

I've wondered about it too, but I think it might just come down to it's far easier to say "papers, please" and verify them, versus auditing a business to understand where their payroll is going. You also need to account for people using stolen/borrowed credentials to appear to be able to work legally in the US(and generally verified by the federal government). If someone says they are Bob Jones, and they show you an ID, and you send that to the government and the government says Bob Jones can work for you, then you have no real way to tell that Bob Jones actually holds 40 different jobs simultaneously all over the country - but the government does.