This is because the classification was preserved after ages, where whether he was an original bushi or not depended on whether his family business was part of the cavalry fighting or not, even though fighting by group on foot became mainstream and cavalry fighting became relatively limited at the war scenes after the period of the Northern and Southern Courts when the number of recruitments to the battlefield dramatically increased.
これは南北朝時代以降、戦場への動員人数が激増して徒歩での集団戦が主体となり、騎馬戦闘を行う戦闘局面が比較的限定されるようになっても、本来の武士であるか否かは騎馬戦闘を家業とするか層か否かという基準での線引きが後世まで保持されていったためである。