Why don't they follow the Master Nichiren

“The Buddha says determining the future, “Depend upon the teaching, not upon the people. Bodhisattva Nagarjuna says, “If one depends upon the scripture it is a correct argument; if one does not depend upon the scripture it is an incorrect argument.” T’ien-t’ai says, “Again, if it conforms to the scripture, quote and use it. If there is no corresponding sentence or corresponding meaning, then one should not believe and accept. ” Dengyo says, “Depend upon what the Buddha taught, not upon the oral tradition.” If one follows these scriptures, treatises and commentaries, then one should not base oneself on dreams. Once should only treasure the passages in the scriptures and treatises…” -- The Selection of the Time

"Answer: Are those who have received the teachings directly from their teacher invariably free from error, while those who appear in later ages and examine and clarify these teachings are to be regarded as worthless? If so, then should we throw away the sutras and instead rely upon the four ranks of bodhisattvas? Should a person throw away the deed of transfer received from his father and mother and instead depend upon oral transmissions? Are the written commentaries of the Great Teacher Dengyo so much trash, and the oral traditions handed down from the Great Teacher Jikaku the only guide to truth?" -- On Attaining Buddhhood in One's Present Form.

"It is also laid down that one should “rely on sutras that are complete and final and not on those that are not complete and final.” We must therefore look carefully among the sutras to determine which arecomplete and final and which are not and put our faith in the former Bodhisattva Nāgārjuna in his Commentary on the Ten Stages Sutra states, “Do not rely on treatises that distort the sutras; rely on those that are faithful to the sutras.” The Great Teacher T’ien-t’ai says, “That which accords with the sutras is to be written down and made available. But put no faith in anything that in word or meaning fails to do so.” The Great Teacher Dengyō says, “Depend upon the preachings of the Buddha, and do not put faith in traditions handed down orally.” Enchin, also known as the Great Teacher Chishō, says, “In transmitting the teachings, rely on the written words [of scriptures].” -- Opening the Eyes