The article states that most deaths seem to happen in the decent, rather than the ascent. This shows that the risk is climbers pushing themselves too hard. This just, well, seems obvious. There is ego on the line, if not other factors. The problem of pushing past your limit, such as mountain climbing, past your reserve capability and capacity doesn't clearly manifest itself at the point you've exceeded your capability, it is when you are trying to move back from the edge to a safe point that this becomes clear. The climbers are so focused on reaching the goal it is easy to forget about measuring the capability to get back down.
I've heard that rescue aircraft keep a reserve of fuel on board and once the craft reach this point, they turn back.
It seems that at least some of the climbers don't gauge this properly. Some are lucky. They survive. Others are not as lucky, they are the 1-2 percent statistic of dying on the way down, having pushed too hard.
Down climbing is inherently more difficult than climbing. When you're "up"-climbing you can see your next steps more easily b/c they are closer to your eyes and the slope is at a better angle for watching your steps. You also have your ice axe held like a cane in front of you to arrest any fall, and the distance of the fall from feet to hands is shorter than on the way down.
On the way down, your eyes are much further away from your steps and the slope is angled away from you. Each step is longer, more dynamic and more likely to dislodge some rock / ice / snow. You are also putting a lot more force on each step so your legs can actually get more tired on the way down. When you fall you mostly go to your butt, slide and you need to roll over on your belly to self arrest. By that time you have often picked up so much speed that it's too late.
All these physical factors plus many well documented "horse to barn" psychological factors make down climbing the most dangerous part of the day.
While that all makes sense, it also seems possible that deaths happen on the descent simply because it takes that long above 8,000 feet for cerebral edema to kill you. It seems like, if those were the main issues, the descent below 8,000 feet would not have shown significantly fewer deaths than above.
Your point about the time it takes for HAPE to set in is valid. But I'm pretty sure that times in the death zone vary greatly. Most parties camp at least one night above 8000m and weather / SNAFU's often hold them there for multiple days So the total time above 8000 varies by much more than the half day it takes to walk down.
No doubt though, the death zone could kill people playing ping pong. Yet the down-climbing problem is global to mountains of any size. The extreme altitude on Everest amplifies it. More accidents occur on the way down on mountains less than half the size of Everest. The mountaineering bible, "Freedom of the Hills" discusses the phenomenon extensively:
This is very true. To see this firsthand, try hiking a steep trail of any significant distance (a few miles). Going up isn't so bad. Its like climbing stairs. Coming down is terrible, though. It is very taxing on the joints and much easier to slip over loose gravel.
Supposedly if you're out riding a horse for a long time and you point him toward his barn, he'll rush home and not listen to you b/c he wants to rest.
It's a common problem among mountaineers that once the "goal" has been reached they rush home and make careless mistakes. They rush down "like a horse to a barn"
I've seen this problems in many different expedition sports. Once the perceived danger is past, people let their guard down and get hurt. More often than not people train for the hardest part of an expedition. They put so much effort into getting through that part, that when it's over their brain says, "I've done the hard part, the rest is a foregone conclusion." They forget that the uncertainty of their goal made them fearful which in turn made them concentrate. Once people feel more certain, the fear subsides and takes their concentration with it.
I've heard that rescue aircraft keep a reserve of fuel on board and once the craft reach this point, they turn back. It seems that at least some of the climbers don't gauge this properly. Some are lucky. They survive. Others are not as lucky, they are the 1-2 percent statistic of dying on the way down, having pushed too hard.