Human Nature ? Or Learned Behavior ?

I would like to ask the yahoo community a simple question that I have been asking myself for the past few days. OK here goes. I really cant figure out why 50% of the people whom which I encounter fail to acknowledge my presence when walking by and the other 50% of people do acknowledge my presence when walking by. Maybe I am being to philosophical about the situation but i must ask. Personally, I always acknowledge everyones presence when I walk by them even if I dont know the person. I do this primarily due to the fact that you never know who you are encountering and may be of some importance to you later on in life. In addition, its also just the right thing to do. I for one am a fairly successful person ( With no ego )in my opinion, and am willing to help people take the careers to the next level. However, I am astonished at the fact that 50% of people whom which I encounter never even take the time give simple courtesy acknowledgement when walking by. Is this due to the fact that people are becoming more and more individualistic as the years go by and more concerned about themselves and their wants, or maybe im just over thinking this situation. However, I would like to end with this: With me knowing the fact that I have obtained the majority of my success through learning from and meeting new people, it seems odd to me that people do in fact block themselves from learning more about lifes experiences from other people who might give them some advice that could change their lives. Hopefully people will one day learn to respect everyone despite their race,ideology and differences.