Yes what? even in real life you don't have this point of view while wearing a mask.
Thera are many kind of helmets IRL and in MO2, I don't need to show you every single one in order to highlight that many of them will block your vision in some degree, one more than others, not in the same way the one he showed us, afterall that was just one example. So you should review your concepts about helmets.
This one is similar to the mercenary armor in MO2. Are you sure you have a perfect filed of view with that?
Either way, it would be a trade-off against higher defence vs field of view. This could be the beginning of a reason to wear other kind of armors in this game. Currently we always see the same armors in battle.
So, in the same way, I would like to ask you No why? I'm not satisfied with the previous answer.