That is because Yoritomo killed many of his brothers in the same clan, and rarely led an army himself (though he was said to be excellent at martial arts, did not show a distinguished achievement as war commander), but did achieve the establishment of the Kamakura bakufu mainly by political negotiation.
それは、多くの同族兄弟を殺し、自ら兵を率いることが少なく（頼朝自身は武芸は長けていたといわれるが、戦闘指揮官としては格別の実績を示していない）、主に政治的交渉で鎌倉幕府の樹立を成し遂げたことによる。