If you are caught having undocumented workers in your employ nothing happens to you only them. Why?

Because the government has to prove the employer didn't follow legal hiring guidelines/laws/regulations.

At the same time, the government tells the employer that if a form is filled out correctly, it has to be accepted as valid - even if the employer knows otherwise.

So even if the employer KNOW somebody is giving false information on the I9 ... if they have the official pieces of ID, the employer has to accept it as valid - or face punishment by the government.

This makes it virtually impossible for the government to punish employers.