The two are related, because one major pillar of activism around "modern slavery" is based on opposition to sex work (the others being prurient interest, a kind of western saviour syndrome, and it being lucrative).

One random link I followed from the Wikipedia article is the source for the statement "Europe has the highest number of sex slaves per capita in the world". http://realstars.eu/for-fair-sex/ The page prominently advocates for the Nordic model.