The general populous is very uneducated about sexual health, risks, transmission rates. I find working girls (who arent fresh off the boat) generally have a very basic knowledge about these things.
Even if they think Prep is the magical protection, it will not protect against a host of STI's.
I think some people are closed minded as well, come up to a conclusion about something (or perhaps their 'mate' who escorts told them) and then believe it.
That is why its also up to the Punter to also take responsibility and not leave it solely to the SP. I have read and met some SP who are absolutely reckless because their knowledge on STI's is bordering on nonsense.
I also read the line that if the 'punter looks clean' then all will be OK with BB or I only did BB with you