Why don't the French smile at strangers? As the French see it, there is no real reason to smile at a stranger. A stranger is someone you don't know and have never met. Why would you smile at someone you know nothing about? Smiling is not taught in French families or in schools like it is in the US. In fact the French don't have a word for friendly as we would define it. The word "amical" is as close as it gets but it is used to define what a person is not- like not hostile.
Bottom line- For the French there needs to be a good reason to smile- seeing a loved one, sharing something in common, a good joke, but not "just to be friendly". That just isn't the French way!
The French people we know and have met are kind, helpful, and caring people. They just have a different view of how to greet strangers and what it means to be "friendly"!
Our insight is based on our limited experience with French people and on our reading of a very interesting book by Polly Platt called "French or Foe". We welcome other opinions and comments on this topic!