The decriminalization actually helped weed out most of the small "street pimps" and violent or non-paying Johns/Janes are now a lot more regularly reported and prosecuted, especially since prostitutes can now actually go to the police without fear of being charged for prostitution.
Legal prostitution also means brothels are now registered as legal businesses a lot more often, which in turn means they have to follow health and safety regulations and are subject to inspections. Before, the state only ever could raid a brothel (illegal by definition) and shut it down, at which point it often popped up again in some new place. This also means brothel operators can invest in their properties, thereby usually improving the physical working conditions as well.
But admittedly it hardly put a dent into the larger criminal enterprises which have an entire "supply chain" incl human trafficking and (illegal) brothels with sex slaves. Those criminal organizations just continued as usual, maybe even profiting from generally increased demand in prostitution now that it is legal, keeping their enslaved people in check with fear and outright violence, but are helped by trafficked sex workers nowadays originating from non-EU states which means those people would have to worry about deportation (aside from violent retribution by the criminal enterprises) if they went to the police.
Now that the state has freed up some resources it previously spent on prosecuting sex workers and their customers, I'd like to see those resources go towards fighting those larger criminal enterprises, but that didn't really happen yet as far as I can tell. There have been some high profile busts, but not more than it used to be.