Why are guys attracted to the "hard to get"?

Why are guys attracted to the hard to get?
I am a firm believer that one should not "play hard to get". However time and time again, I've noticed that guys appear to try harder when the girl isn't too sure about them.

This is frustrating because that means women always end up with the guys they're not sure about chasing them and the guys they are sure about playing games or not being interested.

Like is this an issue of self-esteem? Do guys not feel like they deserve a women's interest upfront? Are guys used to chasing and feel like things were too easy (like they haven't won a prize) if they haven't chased? Why are things like this? Why are guys like this?
Why are guys attracted to the "hard to get"?
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