You're reading a bunch in that didn't happen to my knowledge, especially with korean prostitution as it often happened at the time. I have no idea where you got all that. They weren't addicted to any drugs. There was no one controlling them by violence (at least on any day to day basis). Their parents are likely not involved - korea has a very particular pattern to prostitution specific to it. So all these details you just made up aren't accurate.

The real danger comes from the customers who can get violent. If that happens, who do they turn to? The cops? LOL. Nope, the cops are just as likely to hurt them worse given what happened.

In this case, yes, the cops make things MUCH worse because all of that can only happen with the cops being corrupt.

And no, they don't have to put the girls in jail. The cops (and the prosecutors) have HUGE discretion in what they enforce and how they enforce it. They definitely don't have to use their power to abuse the girls.