Do really pretty girls get approached less?

My best friend is absolutely beautiful both inside and out. Everyone keeps showering her with compliments almost all the time. But I don't understand why she hardly gets approached by men. Last week she came to me saying that she feels insecure because men rarely approach her. I have also noticed this and since then I've been wondering about it as well. Even the guys i'm friends with told me that they find my best friend pretty yet none of them have ever made a move on her. P.S she's really introverted and rarely talks with the opposite sex. I wonder if this is one of the reasons.

Edit:Thanks for the opinion guys,I got a clear picture of it!