Why should the bow and arrow rope be made of beef tendon?

The elastic force of the bow should come entirely from the bow arm, but the malleable string will reduce the efficiency and accuracy.

Therefore, the ancient bowstring was limited by the use of malleable materials such as hemp, while the modern bowstring used almost inelastic materials such as dacromet.

As for bowstring made of beef tendon ... I am ignorant and have never heard of it.