Why do you men stare and never approach?

Question: I get stared at, smiled at, talked to, on a daily basis, but then you guys don’t follow through, ever (well, except, the sleazy ones, with their perverted lines…egh).
Why are you so afraid of rejection? Is it so bad? I’m really asking; I’m sure it’s not the greatest.
Am I giving off an uninterested vibe? I do empathize with the pressure men have on them and would love to do my part but 1) Not sure the best associations are made with women who are forward and 2) I would have no idea how to be…haven’t been socialized to take that role.

I am a very attractive 20 something year old who rarely is asked out and I am wondering if it’s me or if it’s just tough for all of us.

The latest example…though I have thousands:
I’m a student who’s riding the bus with mostly other students and it’s a pretty safe arena for socializing. Every time I look up, cute guy (looks like a Business student, probably late 20s) is looking at me. I smile, he smiles This happens several times over the course of 15 minutes or so. Then we get off at the same stop. I’m walking along side him…he looks really stressed like he’s contemplating his move (awww). We stop at a crosswalk, waiting. eye contact, smile…he quickly turns away, then I see him take a deep breath, turn, look at me, fearfully and sweetly says “How are you doing today?” Me: “I’m good, how are you?” Him: “I’m good. So, are you on your way home?” Me: “Almost, one more thing to take care of, then yes, finally. You?”
“Yeah, that’s it for me…long day.” Me: “Yeah…” Him: SMILE Me: SMILE
Him: WALKS AWAY.

Something equivalent to this happens daily; I mean at least once a day every single day. (and these are not just conversations due to boredom that I interpret wrong; the attraction is clear)
Help me help you. I know it’s hard. I know it may seem like attractive women hear it all the time and are uninterested…not always true!. what should i do to help? Do you need a clear sign of interest, what is a clear sign of interest? I’m not a very smiley person and seem very confident, maybe this translates to snobbish?
wow…post too early in the morning and you get some real crankiness and bitterness. Please have your morning coffe before getting online in the future.
I will rephrase the title: Secure, mature men and women only, please reply to: Why men often stare and never approach?

the mention of my attractiveness (subjective, granted) is unfortuantely very relevant to this society and ceartinly to this question.

Thanks:)