It's likely an artifact of the samurai fighting style which is quite different from conventional continental fighting as experienced by regular troops.
Can you briefly describe the style of fighting that makes this sort of headgear practical?
For one thing, despite their cool swords, I understand that the Samurai preferred to kill people with arrows when possible. They were all accoplished archers, including firing from horseback, which, as we all know from the Mongols, is a very effective way of defeating non-mounted foes.