Girls stare, but never approach. Why?

Anonymous
Often while going out in public. I see women staring at me with the contemplation of lust in their eyes. It's the basic stare down that many see often. It happens quite often (Not to be egotistical), and it is rare for girls to really approach me. I like to do a lot of public things by myself, and therefore are never truly in groups when shopping, or writing my book at cafes. So, I'm starting to wonder why girls stare, and never try approaching. It has even come to my attention that some stare off and on for a good 5 minutes or so, and still never make the attempt.

Side Note: I've been told that I am intimidating to approach, but yet I try to always have a friendly face, and smile when appropriate.

Women- Why do you rarely even consider the idea of approaching a man, and what does the guy need to do for him to become more approachable?

Men- What do you do to be more welcoming towards a woman's approach?
Girls stare, but never approach. Why?
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