The US isn't a dumptruck you can throw blanket assessments on; it's a series of states with their own laws that extend those set federally.
Besides, I think the main issue isn't that there aren't laws setup to protect workers, it's that they are often poorly enforced. Enforcement is carried out by state and federal attourneys general, and by individual lawsuits initiated by the public. Perhaps other countries are better at enforcement, or maybe the public is less inclined to put up with unfair practices.
But keep in mind, there is an active slave trade in all developed countries, so presuming the infallibility of a certain type of government or framework of law isn't realistic.