Wikidata, chances are that they have links to one or more external resources. The picture to the right shows how DBpedia is connected to even more external resources. As you may know, DBpedia and Wikidata also have a very tight connection.
In a way, this can be compared to the many connections Wikidata has to the categories in the many Wikipedias, in Commons. All of them have structure of some kind. Information is inferred and acted upon. The category "United States Army Medal of Honor recipients" refers to people who received the Medal of honor.
When Wikidata is linked to external sources, these links have to be there for a reason. It can be to compare information or it can be to add missing information either way. Applications based on the ontology structure of the external sources can apply their logic on Wikidata.
Yes, there may be a purpose for yet another ontology structure in Wikidata. It may allow for implied information in tools native to Wikidata. But there is no point to all of them when we do not make use of them.