This question was posed by a man with his lovely lady, strangers to me until I warmly greeted them on a pathway along the ocean front of Pebble Beach, a breadth taking scenic setting on the central California coast.
The answer as to why so few people commonly smile is simple. Many people don't realize they aren't smiling as they are caught up in their concerns with every day life.
But the irony is that every day life would go so much better for them if only they would smile more because people in general would treat them better.
So please give it some thought and then put a smile on your face. Whether you are in Pebble Beach, your office or your local grocery store, you will discover that if you smile, much of the world will smile back at you, and treat you accordingly.