I came to North America from Europe where it is polite that people greet each other. The rule of politeness in Europe is: younger greets older, man greets woman. In Europe, children always greet adults they know in a nice, loud, clear voice, looking into the eyes.
In North America, I am sometimes shocked, that children of my neighbor, who know me and even baby-sit for my child sometimes, will meet me on the street and not say a word. I meet fathers of other children at my son's game, and they never say hello to me first. I find it highly offensive if a child or man the same age as me, does not acknowledge me. I am forced to say hello first, because it is extremely rude to just ignore each other.
Please explain this to me.
Don't take lack of politeness as a personal insult. There is a big difference between Europe and North America on many etiquette matters. Keep in mind, Europe is long on history and tradition, often dating back thousands of years. The United States and Canada are relatively new countries by comparison, and only a few hundred years old.
Formality in North America is very lax compared to Europe. You might have noticed that people dress more casually in Canada/U.S. compared to Europe. People in the U.S. are much less formal in their greetings as well. There is no set rule for who greets whom first. Don't be offended by young people or men not greeting you first. Be aware of the cultural differences and go ahead and initiate the first greeting.