Why were some adult nobles in the Warring States period of Japan allowed to go without a Tsukiyo head?

The Tsukiyo head refers to the head style worn by ancient Japanese samurai, because hair tends to fall out for various reasons during war fights, and that's when those hairs in the center-front of the head cover the face, blocking vision and interfering with the fight.

So if you are not going to the front line, there is no need to stay.