Why do women who initially seemed extremely into you, act as if they don’t know you if you approach them too late?

I’ve noticed many times girls gave signs for me to make a move. For whatever reason I didn’t (maybe I was taken at the time) but later I attempt to reconnect and respark what was. It seems at that point they don’t even want to know you and when you suggest anything vaguely romantic they become insultingly dismissive. Why is this?
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