why do westerns say hi to each other, we dont

I am writing now from the USA. I came few days ago to celebrate the graduation and marriage of my brother in law.
I was walking early morning , trying to enjoy the good weather and noticed that everyone, young and old people, females and males.... say hi to each other, even if they dont know the other person.
It s great. i like it. and started thinking why we dont do the same... Our culture is more family and society oriented than their culture. Our religion asks us to do so... why i dont know who is my neighbour? why if i say good morning when i am in the lift, no one replies to me?

small gesture, but it means a lot...
worth give it a thought.