That's only really in jurisdictions where it's illegal. It just comes with the criminal aspect. In Holland they even have a union called the red thread.
From [0]:
> Our empirical analysis for a cross-section of up to 150 countries shows that the scale effect dominates the substitution effect. On average, countries where prostitution is legal experience larger reported human trafficking inflows.
[0] https://www.sciencedirect.com/science/article/pii/S0305750X1...