I personally had a similar sort of a question when I first went through similar kind of stats about these mountains. Getting introduced to these stats is different than totally understanding the mountain and the Pandora's box it opens. For getting acquainted with the reasons for so many failed attempts, one needs to read tactical data and expedition reports. Understanding the weather is important because many times bad weather has made a walk in a park kind of a summit go horribly wrong.
Logistics and Supplies:
Along with the weather, the location can make a mountain more difficult. These big tough-to-climb mountains are not easily approachable. Consequently, many a times you find the local support (labor would be an inappropriate term to use for these great people) like Sherpas and Porters tough to find, fund and convince to come. So things are too difficult with limited support.
If you compare population of these local services around Mt. Everest with other mountains like K2, Kanchenjunga, etc, you would definitely get higher numbers for Mt. Everest, Lhotse and Cho Oyu. Maybe that is one of the crucial reasons for higher ratio of successful summit attempts to failed attempts. It would be wrong to correlate this ratio with "The Death to Summit Ratio". Many times at these great mountains, a failed attempt is death and vice versa. And there is a significant number of expeditions where people actually made a summit and unfortunately passed away on the way down the mountain. After all, it;s not only about standing humbly on the summit, but its more about being there at the top tip and get down the goddamn mountain.
Some Technical Data
One of the factors that makes K2 so challenging is the sustained technical difficulty. Period! It is like a cone of ice and limestone, and has slopes of 45° or more. Climbers typically fix up to 2,500 meters of rope on the south side routes, and up to 5,000 meters of rope on the north ridge route. It is a consistently steep pyramid, dropping quickly in almost all directions. Speaking of the weather, the sudden storms are caused in part because the peak is so much higher than the mountains around it; it juts up into the upper layers of the atmosphere and like a rock in a river can create eddies in the jet stream, with good weather on one side of the mountain, and life-threatening conditions on the other. That is not exactly the case for Mt. Everest, it being surrounded by another 2 Eight-Thousanders.
Speaking of technical difficulties:
That said, its a fact that Mt. Everest is not a walk-in-a-park and Any-Rich-Tom-Dick-Harry-can-summit thing either, but apart from void weather and a moderately difficult ice wall before "Hillary's Step", Mt. Everest unarguably put much less challenges to a summit-optimist at higher shoulders of the mountain where rescue is difficult and unlikely, as compared to that of K2, Eiger, etc.
K2 has its own agenda to deny a summit by means of Serac and Bottleneck above Camp IV. There is no need to even comment about how tough it is. Once Chris Bonington was asked what makes K2 such a tough mountain to climb, more so than Mt. Everest. He had replied, "It's enormous, very high, incredibly steep and much further north than Everest which means it attracts notoriously bad weather."
On the North Face of the Eiger there are 2 technical challenges much talked about.
One of them is called "Hinterstoisser traverse" named after Andreas Hinterstoisser and the other one is called "The Traverse of the Gods". Personally, my jaw dropped when I first watched a documentary on Eiger North Face route. All the north faces in the Swiss Alps were already climbed, but Eiger had parried away all attempts until it was first climbed on July 24, 1938 by Anderl Heckmair, Ludwig Vörg, Heinrich Harrer and Fritz Kasparek in a German–Austrian party.
I have not read and studied much about Nanga Parbat, so it will be inappropriate to comment about the technical difficulties it offers.
For Annapurna the technical difficulty is considered to be graded over Hard Severe for the climbing parts of it. The fact that it is considered as the one of the most sensitive Avalanche-Prone areas, adds more woes to climbing expeditions.
Overall, the technical difficulty level, Weather, Local Support altogether make world's few mountains tough ones to scale. The same goes without saying for many other mountains in the world which have considerably lower number of successful summits and a relatively dangerous Death to Summit ratio.
TAT (Turn Around Time), Height Gain and Supply Management
Its also interesting to compare the height gained from Base Camp to Summit.
- From Everest Base Camp (South) to Summit: 3484 m.
- From Nanga Parbat Base Camp to Summit: 3800 m (Approximately)
- From Annapurna Base Camp to Summit (Annapurna I): 3961 m
- From K2 Base Camp to Summit: 4711 m
Does the height gain and the distance matter? Yes it does! Because these are all tall mountains and located at a higher altitude, the small change in weather is a major concern and the night sinks in so bad. The actual time for the Summit from the Pre-Summit Camp is a very short time-window. The Expeditions always have (if not, then should have) agreed upon a TAT (Turn Around Time). Turn Around Time is what ethical mountaineers refer to as the time at which every expedition member should turn back to the lower camp, no matter how close the summit is.
This window between Start of the Summit attempt and TAT is substantially favorable for an expedition team in case of Everest as compared to the other mountains.
Once I had gone off-road cycling with my nephew in remote regions.
The kid asked me, "Why haven't you ever climbed that mountain?", pointing at a mountain I didn't know the name of.
I said, "I just may some day. But I haven't because I hadn't seen that before and there is hardly anyone who gets here."