[McKee]

Protective helmets are primarily intended to protect against air-burst artillery. In world war / cold war scenario, this was the greatest threat to dismounted infantry. It's the same reason why flak jackets were made, and why they have large shoulder pads (top-down protection). The idea was you'd be protected in a trench, but still vulnerable to top-down attack so you needed protection from that aspect.

Obviously since the end of the cold war, massed artillery hasn't really been a threat, so ditch the added weight.