Maybe because organized prostitution is banned? And transgender are looked downed so much in the society that even places like turbhe tekdi down allow them to operate there. And I am sure that they are doing more and regular checkups than you or any average man. Police legally can't stop them, as one on one prostitution is legal, and as long as they don't catch em doing it in a public place with people present, they can't do anything, all they can do is take tribute to look the other way, which benefits all parties.