I have not read that and don’t intend to at present, so let’s give you that argument.

I’d propose a simple reason for this. I would imagine a lot of the inflow is from other countries where prostitution is still illegal. Traffickers move them to legal countries, possibly even legal brothels, and coerce the person to stay quiet. Johns don’t have any reason to suspect, because it’s legal, so it may provide safety to the traffickers, in a hiding in plain site way.

Feel free to correct me if I’m wrong, or if the article addresses this in some way. I’ll read it a bit later.