That's the whole point ~ Public toilets are where the rough trade hang out waiting to be "picked up".
It's not really possible for a bloke to walk up to another bloke in a street and say "fancy a quicky?" without risking getting your nose broken.
In the public toilets there are locks on doors so that the act can, with luck, be private. Hardly give someone a blowjob in the street can you? A wink and a nod to someone in the gents is the usual pick-up and straight into a cubicle.
As for Soho ~ it's a fvking long way to go for a w@nk if you happen to be in Gloucester at the time the mood strikes.

I know the whole thing makes some of you

but accept it happens. If you don't fancy it then a simple "No Thanks" is all that is required.