Though I have no problem with the way Predators are currently designed, but recently I have wondered why they don't wear more armor.
I suppose one reason is they full confidence to stay hidden, so it's not usually an issue at the front of their mind. Another idea I had is, Predator's like to purposely out themselves at a disadvantage with exposing their arms, legs, chest. To make the hunt more thrilling and challenging.
But with City Hunter taking 4-5 shotgun shells at close range, and surviving to fight on with ease. I guess the most logical explanation is they can pretty much tank crazy amounts of wounds.