Could be several factors but here's a bit of insight to the female psych. From the time we're able to talk and walk we are taught that we need to be everyone we come across. At least that's how I was raised. When a stranger passes, you smile and say hello or smile and wave if there's glass seperating you. We don't always remember to do this cause as you can imagine, it gets very tiring but we do remember it most of the time.