Mr Niedenthal died recently. It is not known on what date exactly but he died in July 2014. According to the article about him he was a member of the German Bundestag.
As I am adding information about the people who died in 2014, it is possible to add statements for one person or start adding one statement for the many people who are in the same category. When a party member of Mr Niedenthal died recently, membership to his party was added for many people including Mr Niedenthal.
Given that the lack of data is holding back Wikidata the most, it is a strategy that seems to be working. If there is one draw back it is that those languages where people are categorised by the year they died benefit the most. The Dutch Wikipedia for instance does not and consequently the items represented there do not get the same treatment.