That's why we have laws of general application. Forcing someone to have sex for money, or not money, is sexual assault—period. We need to enforce that, and then the list goes on.
In order to commit a trafficking offence, you need to commit a lot of other offences. Those are sufficient in most cases. It's actually quite insulting to a lot of victims when sometimes they've gone through extreme violence and the only charge is human trafficking, or the only charge is pimping, and not every act of violence. If we start prosecuting those, we'll start seeing the repression that we need against that type of violence.