Some (most?) Western countries explicitly have laws against this. Fun aside: I used to work at a student library and management was very clear about us not being allowed to retain government-issued personal ID cards as collateral (instead of the university-issued student ID cards) because doing so would be breaking the law.

Of course human traffickers don't care about the legality of the practice, but there's a difference between something being widespread among criminals and something being culturally (or legally) acceptable without having to buy off police or customs.