Yeah, that defacto slave labor really cuts down on the overhead. Not to mention the cost savings Inherent in not having to deal with pesky things like worker health and safety.
It isn't just that. Over the last 50 years, the US has steadily increased the cost and liability of labor on top of higher corporate tax rates. The tax rates were helped with the tax cuts Trump signed, but the cost of labor is still high (relative to what I don't know).
And by cost of labor, I am not just talking about pay. There is health care, unemployment, worker's compensation, payroll taxes, injury liability, regulatory compliance, etc, etc.