Why do girls give guys false hope?

OK so this happened to me twice and it happened to a bunch of my friends. we ask a girl out or just happen to stumble on the subject of dating together and the girl says "oh we might be together you never know" or "you'll have to prove that you're not just a lazy guy" and then when we (the guys) try to show them or try to spark it and flirting with the girls (while they flirt back) they just end up saying something like "oh I'm dating this guy... it just kind of happened." I really don't understand why girls play with guys like that, can you girls answer why you do that? ( I understand not all of you do no offense)
Why do girls give guys false hope?
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