Because Facebook doesn't give you what they really know. The download-your-data feature for a time showed the truth, in 2013: http://www.zdnet.com/article/firm

Because Facebook doesn't give you what they really know. The download-your-data feature for a time showed the truth, in 2013: http://www.zdnet.com/article/firm-facebooks-shadow-profiles-are-frightening-dossiers-on-everyone/ http://www.zdnet.com/article/firm-facebooks-shadow-profiles-... So we may presume FB, especially in the US with little-to-no privacy laws against corporations, won't tell you what the really know.