six degrees of separation" made popular around Kevin Bacon has its scientific approach in graph theory "betweenness centrality". This is used as a basis in the research that what articles are important and what automated suggestions to make.
Mr Putnam is one of the more relevant librarians. He developed an eponymous classification system, continued its development as the Librarian of Congress (it is still in use), was twice president of the American Library Association and was a knight of the order of the Polar Star. When weight is applied to references to a person, all this is of relevance in the right setting.
When an article is to be written or improved, it helps when it can be suggested what it is that can be improved. By including statements in Wikidata suggestions can be made based in the local language. Facts like date of birth and death are also easy and obvious.
So when people consider a particular subject to be of universal relevance, it helps when associated subjects are well developed in Wikidata. When for all the presidents of the American Library Association many facts like where they studied, where they worked and what awards they received are included. When this is done for all the people who share categories, the betweenness of many influential librarians increases. This will have its influence on what is suggested for people to do.