The Alzheimer's info is rather old, but still basically accurate. Although it's theoretically possible for an advanced case to finally shut down a brain center that controls an essential function, patients seldom live long enough to reach that point. They fall, cut themselves, get food in their lungs, and do all sorts of "dumb" things that result in an infection. Eventually one gets out of control and kills them. Quite sensibly, there's not a lot of motivation for heroic measures to save them.
On the other hand, as the cancer info says, this one kills in myriad ways. It depends on what system it affects. One common course is for it to overwhelm an organ so it can't perform a vital function. The article points out that a great many cancer patients survive more than five years. Of course this is wonderful for the patient and his loved ones. But notice that nobody talks about the ten-year cancer survival rate.
I have a friend who's in his seventh year with bone cancer. On the other hand, 35 years ago a dear friend with cervical cancer was gone in barely one year.