"despite slavery now being illegal in every nation on Earth"
I can think of one nation where slavery remains legal: the United States. The 13th Amendment abolished chattel slavery, but it contains an exception allowing someone to be enslaved as punishment for a crime. Several states still sentence people to terms of hard labour, and even the ones that don't still enforce work on the majority of their prison population. The vast profits made by private corporations from selling and receiving prison labour are the reason why America has the largest prison population in the world and the sixth highest number of prisoners per capita. It is a perpetuation of the slave system in all but name.