In addition, this is also because the battles between different regions did not always happen so, there was no risk to life, and they did not need to improve Yumiya if they could obtain enough food for living.
また常に地域間で戦いがあった訳ではなく、切迫した命の危険がない事と日々の糧が十分得られれば、弓矢を改良する必要がなかったからである。