If helps take less damage overall. It will help them nonetheless. There is no such thing as explosive vests. So, it would be more realistic to provide them with armour. Although its specifically against infantry and does not help against explosives. It will help anyways.
It's not a matter of whether or not it will help them, it's that it helps them against things they don't need help with. They don't need help against small arms, so buffing them against it doesnt make sense. You can't just buff it because you want to, doing that will negatively effect the balance of the overall game