Sorry, but I am slightly confused.
Why is it OK for us to fuck hundreds of prossies but wrong for a prossie to have fucked hundreds of clients.
Because she has effectively, for good or ill, put a price on herself and is available (generally) to anybody willing to meet that price, young or old, good looking or ugly, polite or rude and so on.
That is not the same as somebody making a free choice, by picking and choosing who they see, according to their own personal standards. Mind you, some punters probably have no standards and I've made some bad choices myself!
Yes, there's a little double standard here, but I'm never going to go down on a 65 year old woman for cash, for example! Fuck that. I'm worth more than that. The position of a prossie is somewhat different, is it not?