Because you can always truck in a slew of desperate people willing to work for lower and lower wages until we descend into de facto slavery (not even being hyperbolic, that's essentially what many sweatshops are in some countries, look at hypercapitalist Dubai where companies retain control of 'employee's passports and refuse to return them so employees cannot escape the country/near-fatal working conditions).

We've compromised as a society and said sure slave labor will exist but not in the US, if a company wants to benefit from the infrastructure and educated workforce and culture and benefits that American society has developed they have to be decent corporate citizens and treat workers with a modicum of respect. You're suggesting bringing slave labor here, I'd suggest rather we sprint in the opposite direction and ban it everywhere through e.g. making the import of goods made through slave labor a criminal offense.