At least some of the UN's figures on human trafficking are based on the amount of news reports about it - which, given all the activist groups with good press contacts using it to argue that prostitution should be banned, is not a terribly accurate measure.
Do you know for example that most human trafficking number includes every prostitute that has paid someone for assistance with moving to the Netherlands? Like finding a house, opening a bank account and things like that?
Human trafficking is to prostitution what child porn is to online privacy.