Even in countries where prostitution is legal women are being trafficked against their will to those countries to be forced into sex work.
They’re already being trafficked to the US to be forced into prostitution, why would they care if it’s legalized. It wouldn’t affect their trafficking.
But I also feel you may be inflating the ramifications of legalization of drugs and prostitution. I believe it was Canada or one of the US states where the cost of legally sold Marijuana was still too high and people turned to their old dealers. You’d see the cartel enter the market again with cheaper, more dangerous options for those who can’t afford the higher priced, taxed, and regulated products.
We can regulate those who wish to operate above board, but you can’t stop the pipeline.