You have to remember that in the past a lot of Romanian girls weren't.
Due to the loose way in which Romania handed out ID cards to anyone with the slighest connection to the Austro-Hungarian empire, you ended up with cards being given like sweeties to girls from Belarus, the former Yugoslav states, Moldova, and (especially) Albania.
And because of the existence of Transnistria, Russians could pretend to be Moldovans and get Romanian cards.......
Hence of lot of girls coming into the UK using Romanian ID cards which were legally obtained though not strictly correct.
Essentially Romania felt it should offer EU citizenship to as many unfortunate non-EU residents as it could, and the EE trafficking gangs took advantage.
One of the effects of Brexit is that the UK no longer accepts EU ID cards for transit: full passports are required. Romania doesn't hand those out with the same degree of freedom, and obviously they cost a lot more so the girls and gangs no longer have an easy route into the UK
Also remember that with Brexit it's no longer possible for girls to arrive, then get part-time jobs working in Tescos for 5-10 hours a week so making it look like they're really working (or else signing on the dole), and using that as a disguise for money laundering sex work.
You'll see now that the Romanians now working the the UK now tend to be older girls (no longer the 18-23 age group) who've been here some years and have attained legal residence status here. Same goes for the Hungarians and Bulgarians still here - most of whom are exactly what they say they are, Hungarian and Bulgarian (though predominantly gypsy)