The reason Yoshitomo followed Nobuyori was that Nobuyori was the Musashi no kami (the feudal lord of Musashi Province) while Yoshitomo was extending his power in the southern Kanto area and later became chigyo-kokushu (a provincial proprietor with the authority to appoint a provincial governor and collect tax).
義朝が信頼に従ったのは信頼は義朝が南関東で勢力を拡大していたときの武蔵守でその後も知行国主であって、