As I understand it [1], usually if you try to cross the border declaring you intend to engage in sex work, they turn you away. Some combination of prudishness and concern about trafficking.
For there to be a special sex worker visa is a surprise, to me.
[1] https://www.pace-society.org/wp-content/uploads/2023/06/3194...
It's strange, but is it really surprising? It's not like hypocrisy and moat building are new things in American politics.
These days I wouldn't even be surprised to discover it was intentional. Some person or group wanted to ensure they could engage in sex trafficking with a superficially legal cover, but didn't want it to actually be legal.