Why do people think that we don't love each other?

We are both 43, and we have been married for 15 years. I am physically unable to have kids, and we have chosen not to adopt or get help to get me pregnant. We have thought about having kids, but we have put our careers first. I have come across many people who have asked if our relationship is dead. It is far from dead. It is just that we don't show public affection (because we are both well-mannered, disciplined people). Why do people think that we don't love each other/are splitting up etc just because we don't show public affection or we don't have kids?