It's because these guys think there is some magical thing they need to say to a woman to convince them to go out with them and if they just figure out what that is (or get someone else to tell them) they'll hook her. It doesn't work that way. A woman will typically know whether she wants to spend time with you before you ask her out. Then it doesn't matter what you say (as long as it's not completely stupid or arrogant), just that you've made a move. Of course, if the first thing you ever say to her is "want to go out?" your chances are a bit low (but by no means zero).
Of course, sometimes she might say no and eventually change her mind, but you have to make your interest known pretty quickly, or you get stuck in the friend (i.e. "no fucking way") zone. So basically the worst possible thing you can do is not ask in the first place.
tl:dr version: Grow a pair.
---------- Post added at 11:09 AM ---------- Previous post was at 11:05 AM ----------
Also, thinking of the female as some unattainable foreign body can't help.
Exactly. You're looking around your classroom thinking "I'd hit that". The women (being, you know, people) are doing the exact same thing. If you're on that list, she will say yes when you ask her out. If not, she was never going to.