China Bans Wikipedia - But Why?

Wikipedia has an article listing a slew of websites blocked in mainland China. The latest entry: Wikipedia. China has expanded its ban on Wikipedia to block the community-edited online encyclopedia in all available languages according to BBC reports. An earlier enforced ban barred Internet users from viewing the Chinese version, as well as the pages for sensitive search terms such as the Dalai Lama and the Tiananmen massacre. But why?