Because FUJIWARA no Fuhito played the major role in `the Taika Reforms,' only Fuhito of NAKATOMI no Kamatari's sons were granted the family name of Fujiwara.
藤原不比等が「大化の改新」の主役だから中臣鎌足の息子のうち不比等だけが藤原姓なのである。