By the way, the information about the percentage came from an Ancestry.com Survey that was published back in 2007 so the findings are hardly new news. See "Survey Reveals Americans’ Surprising Lack of Family Knowledge."
Why is this the case? What difference does it make? A number of recent news articles have commented on the fact that Americans generally put family first ahead of country or religion. If we predominately put family first, why do we not know more about our families? I realize that my readership is primarily genealogists who can rattle off generations of ancestors, but what is there about our American culture that values family be doesn't seem to value it enough to remember their names?
Obviously, I am not a test case. I am doubly fortunate that my immediate ancestors had names that are easily remembered. But the issue of knowing the names of ancestors is only a shadow of the greater issue the encompasses the loss of generational traditions and culture. Nationwide, the national marriage rate is going down from 8.2 per 1000 in the year 2000 to 6.9 per 1000 in 2017. At the same time, it is estimated that about half of all the women have cohabited by age 30. See "New Report Sheds Light on Trends and Patterns in Marriage, Divorce, and Cohabitation." The rate of divorce has dropped slightly from 4.0 per 1000 to about 3.2 per 1000. See "Marriages and Divorces, divorcestatistics.org." It is entirely possible that the drop in the divorce rate is due to the rise in cohabitation and the drop in the marriage rate. What does this have to do with genealogy?
Think about the trouble you have had in finding the records of a mobile single person in the United States. How do you track someone who lives with a partner but does not get married especially if they continue to keep their single names and bank accounts etc? Do these statistics seem to indicate that there might be a problem with children from such homes knowing the identity of their grandparents?
As genealogists, we may feel insulated from the disintegration of the American family, but in reality, these statistics translate into a genealogical nightmare. A child raised by an unmarried couple may have no real concept of generational relationships and divorces likely result in separation not only from a parent but also from the separated parent's family.
One of the things we can do is to try to record the relationships and families of the present time as much as possible even if the participants are not interested in family or ancestral relationships. Remember, a cohabitation arrangement does not produce any marriage or divorce records. It is also possible that the parentage of children born in these relationships will be hard to discover in the future. Perhaps genealogists, rather than be so focused on the past need to look to the future. In the past, there was a strong tradition of preserving family information in a family Bible or other writing and maybe we need to start preserving the memory of these people in our own way.