According to Provisional number of marriages and marriage rate: United States, 2000-2011, marriage rate in US is going down. (HERE)
In 2000, the rate was 8.2 per 1000 people.
In 2011, the rate was 6.8 per 1000 people.
If this trend continues, in 2020, the rate can be near 7 per 1000 people.
I don’t know how long I can live, but if I can live up to 90 years old.
Marriage rate can be 1 or 2 per 1000 people.
If my children happen to be married in next 10 or 20 years, they can be 5 or 6 out of 1000 people who are married. It is possible that if my children have kids, they can live in a world where no one out of 1000 people get married. It can be 8 or 9 per 10000 people instead of 1000.
Think of the long term effect marriage rate has in terms of birth rate, mortality rate, and the viability of human civilization.