LADIES ONLY: whats wrong with you approaching a guy if you like him?

i have some lady friends who that if they like a guy they will send him little signals like walking by him a couple of times or all of that stuff women do then they said that if the guy wouldnt pick up on the signals then they would just go on about there business but my question is why not just approach him and talk why do women have to send discreet little signals?