Employers who knowingly employ illegal workers in the US also get in trouble. However, we also have a system called e-verify which handles checking the employability of people for them. It's relatively easily gamed via identity fraud.
If this were true -- if they were actually punished (eg sent to prison for N years) -- the whole problem would solve itself overnight.
They might get a slap on the wrist fine that probably doesn't even negate the profits off the illegal labor.
> However, we also have a system called e-verify
The majority of states do not require e-verify for most jobs. Many states don't have any requirements for e-verify and a few only have limited requirements.