They usually aren't "employed" though, as far as I know, as in having employment contracts. That's the new thing they're doing in Belgium, they're now entitled to a contract that guarantees adherence to labour laws.
That most sex workers are self-employed in Germany is a result of the strict employment laws, in particular, if you employ a baker and tell them to knead bread and they refuse then you can fire them. Can't do that with a sex worker as they can refuse to serve any client for any or no reason.
It's not like there's no employed sex workers but the more usual model is that a brothel provides a room, security, and a lobby and sex workers pay for the use of those with money they make off their clients. Just like running a business in a mall, but a particular kind of business in a particular kind of mall.
they’re now entitled to a contract that guarantees adherence to labour laws.
Sounds like they're "entitled" to have to find a boss to work for in order to benefit from this law, unless the government provides maternity pay for freelancers?