Quite a feat. 
It’s funny, if you ask him what his secret is on takedown defense, he says it’s really simple: he just makes up his mind that he’s absolutely not going to go down. It looks like all technique to us, but to him it’s all about willpower.
Google “fedor arlovski video slow motion” and watch the first link. It goes by almost too quick to see on regular speed, but in slo-mo you can see Fedor whips Arlovski’s head around good and hard.
I was watching frame by frame. Hmmm, maybe that’s just as far as a person’s head turns to the side. Any ideas about the nerve bundle strike thing?
As for the OP, there’s this:
“Take a BJJ blackbelt and punch him in the face he turns into a brown belt.Punch him again and he becomes a purple belt and again he becomes a blue belt and again he becomes a white belt” -Carlson Gracie
The point being that these guys do get befuddled by getting punched. If you watch a UFC fight, a guy will take a direct punch to the face in the power range of the opponent, and he’ll take a step or two back, and Joe Rogan will yell, “He’s rocked!” This is when the opponent jumps forward and either starts a punch swarm or tries to take him down.
IIRC, the UFC’s “Octagon” cage is 32 feet across, which is an awful lot less than it sounds, especially since you start more or less in the middle.
The other guys have pretty much covered it: it’s hard to land a clean blow, you can’t punch as hard with thinner gloves, many fighters focus on grappling. That last point is a BIG factor.
Every single time I watch a boxing or kickboxing match, I see possibilities for throws, locks, dislocations, leg shots, balance breaks, etc. that are completely ignored because the rules do not allow for that kind of fighting. Disallowing grappling changes everything. Closing distances change, blocking methods change, body mechanics have to change because of the potential for grabbing a limb or disrupting balance.
All of those things limit the possibilities for landing a clean blow, and they also make it difficult to get the kind of windup you see in boxing. Often, those sweet knockout blows are landed as part of a combination. Try doing a combination in MMA, and the guy will probably grab your arm, shoot in on you, or do something to screw up the setup for a big blow. Set yourself for a big hit, and your opponent will use that second as an opportunity to ground you, or use the extra energy you put into the hit to lock you or throw you. So what you get are punches that will still hurt a lot, but usually don’t have knockout potential.
I hope his hand was all right! 
jackdavinci, You posted this immediately after I explained why you can’t throw hard, clean punches straight through your opponent.
If you were to haul off and punch someone, like a very tough and hardened UFC fighter, and tried to punch clean through him, he’d probably remain standing, and you’d be facing submission because you just shattered or fractured several bones in your hand.
Further, if you miss, you could be a dead man when you are grappled off balanced.
It translates to boxing very well, too. Muhammed Ali took down some of the ugliest and most brutal opponents by jabbing them. He didn’t haul off and try to punch clean through them. He actually did much of what you describe with the cat-like action.
I’m not sure of this. While continuous jabs can certainly wear one down, in boxing the jab is generally used to set up KO punches (or score points).
Even Bruce Lee’s straight lead was generally a means to close to within trapping range. His straight blast was a series of head shots, which not only inflicted damage but also occupied and distracted an opponent, giving the attacker the opportunity to close and finish through various means.
I guess this kinda hints at something I thought of responding to the OP.
-Head shots are often of value to an attacker because of the reaction they elicit. Hit a guy in the head and he generally raises his guard to cover his face, opening up his body, groin, and legs. Remember that nearly all techniques are best done in combination. You get a guy to react in any way, it opens up certain lines to exploit with subsequent techniques.
-A head shot will generally take a guy out of his rhythm, which the attacker can also exploit.
-A poke to the nose will often cause a guy’s eyes to water - a blind opponent is generally a good thing.
-Also, shots to the face are the most likely to draw blood as the skin is stretched taut over the head/face bones. Blood really tends to take the fight out of folks IRL, and may lead to a TKO in the octagon.
You question my post (“I’m not sure of this”) then…Well, you’re stating the obvious and confirming what I said. Go back to the OP and understand what the question is all about. Jabs can certainly wear one down. There goes part of the answer, as I have given it. Even in open fighting, jabbing has value. We’ve established many reasons knockout blows are not just a given with these fighters, and we’ve established why short punches, jabs and grappling are effective.
Fine.
I guess I misunderstood what you meant when you said Ali took people down by jabbing them.
It’s a possibility; some martial arts do utilize nerve strikes (and the trigeminal nerve in the face and along the jawline is one of the nerves targeted), but I don’t know how useful they’d be in MMA. My instructor had a demonstration of a leopard punch and claw to a nerve center under the armpit, and it hurt so bad he saw stars and had his arm temporarily paralyzed. The problem in MMA is that the claw would be illegal and a precise targeting strike to a nerve might be too much of a low percentage technique in the ring - hard to pull off against a guy five feet away jumping around like a maniac, and if it didn’t work you would have been better off just punching the guy five times and racking up points with the judges.
More or less what I was going to say. Adding grappling chages the range.
He made a speedy and complete recovery.
It’s not because of limitations; quite the opposite. You can’t “swing for the fences”, because if you do so, your opponent will duck under, grab your legs, and take you down. If a jab has ~5% chance of connecting, why would you risk opening yourself up to make a full-out commitment swing that has a lesser chance of connecting?
There are plenty of knockouts in MMA. But they are not the norm. Most guys who slightly prefer standup will go to the ground if they’re facing a guy who is famous for a strong stand-up and a weak ground game.
You usually only see knockouts when they are between 2 guys who really prefer standup (so much so that even the guy who is 80% standup-20% ground game would prefer to stand up against a Chuck Liddell-type [or in the case where Tito Ortiz felt honor-bound to stand and bang with Chuck because he said he would.])
I recommend watching a few videos of Royce Gracie (or any Gracie) on youtube to see how powerful grappling is.
I’m not sure what you mean by ‘traumatic brain injury’ but having watched a lot of MMA/UFC/WEC, I can tell you that a lot of knockouts come from hitting an opponent when their head is on the ground and does not move.
Yeah I thought about that after I posted. I guess that explains the lack of boxing punches, and the other posts explain the lack of focus on hitting. The one thing that still seems odd is when they are down on the ground, face to face in a partial hold, one thing I notice a lot is the guy on top will kind of swat at the other guys face or ribs, but it gives the appearance that he’s actively trying not to hurt the guy too badly. Maybe it hurts a lot more than it looks, but if not it almost seems like the effort would be better focused on improving the hold than on getting in a couple light swats.
These guys punch as hard as they can without breaking their own hands and fingers. It really is that simple. You can’t punch a guy in the skull with essentially no hand protection and with all your might all the time and not break your hand. And the ribs? Wow. Skull and ribs are some of the toughest things to punch!
You should see what happens when they kick with all their might, straight through an opponents legs. If you whip kick 100%, an your shin contacts his shin, and you catch him on a thicker/stronger part of the shin, don’t be surprised to hear the sound of wood snapping (your leg snapping). There are videos out there of clean leg breaks and compound fractures from landing these kicks.
Guess you need to punch someone in the skull and report back! Or, find something of similar hardness, and punch with all you got. Report back from the E.R.
Those punches to the ribs aren’t going to stop the fight, but I’m pretty sure they do hurt. I think that usually the point of them is to force your opponent to defend them, thereby moving his arm (e.g. stop defending his head and defend his side), giving the rib-puncher an opportunity to improve his hold.
I’m not up on current MMA rules. Why don’t they use the heels of their palms or hammer fists instead of their knucks when striking hard targets such as heads and ribs?
Because it’s really, really hard to land a blow using the heel of the palm or a hammer motion, and a palm strike to somebody’s ribs isn’t going to do much to them anyway.
With tape and gloves, I’m not sure palm heels would give much of an advantage over knuckles, plus it takes away an inch or two of reach and risks a warning if your finger finds its way into their eye. Hammer fists are definitely used, though, especially on the ground.