Good question. They do make some with padding on the chin if that's what you're looking for, but most don't have it for some reason. http://store.titleboxing.com/thgff.html
I have no idea but since no one else seems to have any idea ill give a guess and say it might get in the way of your guard, like the glove sticking or some friction when you throw a punch or move your hand to block.
And thank god. That way its still somewhat possible to get a Ko in the ams. Why not put the whole face plate on there? I don't think the standard head gear offers huge amounts of protection to be honest, your brain still rattles around, I think it just makes going for the kill a bit harder. My nose has been messed up beyond belief with head gear by punches I think I could have avoided with better visibility (ie - always feel like I take more damage with it than without it) But if you are going to throw me in there with someone who is going to hit me whenever they want like Pac, then, heck yes, I'll take any protection you are going to give me. I wouldn't see those punches coming anyway. Having said that the face plate is awesome! I was able to spar physically with 175-180 pound guys with it because my weak spot, my nose, was completely safe and I could actually compete on a strength level once I could take the heavy shots. My face would fall apart without that, though. Nobody seems to have every quality - strong punches and speed always seemed to be cancelled out by a weak punch resistance or something equally destructive like tendency to form gaping wounds from light punches, or really resistant guys who just don't have power, etc.
I've always thought that the main purpose of headgear was to prevent cuts and abrasions on the face, not to pad the blow. I don't think that small amount of padding is going to protect your brain hardly at all, so why have more there to obstruct your vision? Not to mention how uncomfortable headgear with padding over the chin is.
DTrav is absolutely spot on. The intention of a headguard has always been to prevent cuts, mainly cuts caused by clashing heads. The second fallacy is that headguards reduce the impact of an incoming shot, they don't! There are a number of methods for reducing the impact of punches. The most obvious method (other than being a skilled defensive boxer)is....the use of boxing gloves, not the use of headguards.
these pad the blow http://www.totiro-usa.com/category-s/28.htm these too http://winning-usa.com/headgear.html
