You know, I think it really has to do with age. I'd say most people get married in their mid twenties to early thirties. So if the person who wrote that is that age, and we can assume that their friends are also about the same age, then... duh! Obviously when you're 20, most of your friends are focused on school, then starting careers. Makes sense that as you collectively reach a certain age, you all start settling down with someone.