Seriously, they died from carbon dioxide poisoning. WHO KNEW? Well, they SHOULD have.
Mountain climbers are a type of thrill seeker. The taller the mountain, the bigger the thrill. For someone to be able to say, "I climbed Mt. Everest", is a boast few will ever be able to make.
Everest is the ultimate challenge. One doesn't simply pop on a backpack and do a day hike to the top. The climb takes at least 2 months round trip. It's not cheap either. Purchasing all the necessary supplies, equipment and hiring guides can cost upwards of $30k. The air is thin and bitter cold, the ground is covered with snow and ice, winds can be brutally, and the weather can change dramatically in a matter of minutes. To make matters worse, one has to stop every now and then to climitize themselves to breathing the thin air. Even so, there are many who will gladly accept this challenge.
As with all "ultimate" thrill seeking ventures, this one also comes with a risk of death (the odds are low and vary with the age and skill of the climber). Yet, to the true thrill seeker, the odds are well worth the thrill of the adventure and the bragging rights of saying that they've done it.
Yes, many of us think people who climb Everest are stupid. Of course, so are those who skydive, cliff dive, or bungy jump (a lot of "splat" stories there). Everyone who attempts these feats know the risks involved before they start. If they didn't think they could beat the odds, they wouldn't do it. While any death is tragic, these people gambled with their lives and crapped out.