ps I'm not some prude.
Most Helpful Girl
Because they are under the misguided impression that any attention from a guy is good. Then guys come up, chat them up and expect a one night stand and get surprised when most of these girls have no intention of going home with them.
I think when you send off such strong sexual signals like this you attract the wrong type of attention and if you really want a guy to notice you and date you, you are better off looking more like the girl next door than a streetwalker.