I hear it a lot. "I'm so pretty, but guys don't hit on me?" Or "why do guys never hit on the pretty ones?"
There is a reason: because some (not all of course) girls are just cruel. It's usually a loud embarrassing and public rejection. How many of those kind of mean turn downs would it take for a guy to just give up? Not many.
Think about it what how many of these kind of rejections could you take before saying "no, not worth it?"
And I know it's not fair to judge all women by the actions of a few, but how can a guy tell which is which without asking? They can't. So they simply don't.
It's much easier to get rejected online via dating websites, where there is a level of anonymity.
As one guy said, approaching a girl is like a minefield. One wrong word and....