We all sell our bodies for profit. To be fair though, wage theft is the most common form of theft. We're all prostitutes and we're almost all being taken advantage of, and we're in a system where we can't really get out.

government bodies being incompetent at protecting the victims, then.

My guess is that it's just more difficult to control prostitution than it is to control construction work. Construction happens in the open, you need to get tons of permits, multiple companies are involved, inspectors check everything regularly. It would be difficult to force some people to work on a construction site without anyone realizing. But how are you going to make sure that each sexual intercourse in some strip bar is 'legal'? Are you going to put inspectors in bathroom stalls? How can you check every cash transaction? It's pretty much impossible. You can monitor the sex work that's advertised and happening 'in the open' but there will always be some grey and black market for it. And the ugly stuff will happen there.