Why don't all guys stare at me?

This is a stupid/maybe conceited question I know but I am insecure and wondering... I've been told I'm pretty, I get stares from guys in public, I think I am pretty too. But also, most of the time guys aren't staring at me. I sit across some normal dudes on the ctrain or bus and they're not even paying attention to me. Why? Am I ugly actually or are they just whatever?
Why don't all guys stare at me?
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