Slave labour isn't just something from the 19th century... we just outsource it now, to be out of sight so that it isn't visible enough to the general public, who would call for better treatment or payment (like the US Civil war 150 years ago).
Big business and governments just don't want it to be common knowledge because it is more profitable, and keeps inflation (and subsequently wage rates that are pegged to CPI) lower.

It might not be obvious to most people a world away, but we've seen leaked footage and photos/info of what their working conditions are like, and how most are forced to work for 12-18 hours a day and still struggle to cover their basic living expenses (the food, clothing, and accommodation that was given to black slaves in Europe and America in the 18th-19th Centuries). The only difference is that contemporary "slaves" are not executed for trying to leave their masters... but can still be punished, because it would be a breach of contract from signing away their rights just to get the job.

(end of rant from someone who is a strong advocate of fair workers rights)