Why has the Roman helmet no Noseguard?

[Zarathustra]

Maybe it has something to do with the propability of getting hit in a certain way. I figured that the the only part not protected was the nose, if a horizontal strike hit right in front of the eyes, that would likely break the nose. So here would a noseguard really add protection, hence the question. But on the other hand, if such hits were in reality very uncommon the expense of applying a noseguard to all helmets just not justify the expenses.