In competitive recurve bow, why do people use arrows only slightly longer than pulling them?

Only top athletes need to be "just a little bigger than a saw", and most amateurs just imitate it.

Modern recurve bow needs a "clicker" to accurately fix the saw, which can be installed on the aiming rod instead of the bow. The length of an athlete's arrow is slightly longer than the pulling distance, which can make the arrow, bow and athlete's body cooperate perfectly, but ordinary players can't achieve this effect, just imitate it.