Why do girls approach then ignore me?

Girls at work, college, etc. will say "hi" or try to make small talk to start conversations, but either that will eject, or after a little conversation begin playing with their phone. One girl I know came up to me, starts a conversation, then, twice, the minute someone else comes along, turns & starts talking to them. Another asked what I was eating, I answered, then she quickly left & went to sit elsewhere when I tried to talk.

My rule is I'll put in effort 3 times & if it goes nowhere just ignore them, but many times I'll look over & find them staring at me repeatedly & when I walk by them, yet when I try, even if they're talkative with others, they'll come up over time multiple times, try to begin talking to me, then when I engage conversation, as I do fine with men, but girls will repeatedly quickly seem to ignore me, yet stare & approach every so often like they want to talk.

Many of these girls don't have a "mean" reputation either, many genuinely are considered very nice, polite, etc. I just don't get why it happens so often, but only with women & I rarely, if ever, have issues keeping full conversations with men.

Why do girls approach then ignore me?
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