I think cancer scares people more because of the idea of something growing within your body that ultimately can cause your organs to fail, etc. Also because the symptoms can be so elusive/nonspecific. As well as the fact that if caught early, it makes it more curable (unlike diseases like Alzheimer's, MS, Lou Gherig's), which makes us HA people constantly on high alert to find it lurking in us. Another reason I think is that the treatment itself is so awful, both in the aesthetic effects (hair loss) and physical effects (debilitating nausesa, etc.).
Regarding the fact that so many people seem to get cancer, one thing to keep in mind (discussed in H. Gilbert Welch's book Overdiagnosed--highly recommended for HA people) is that, contrary to our intuition, lots of cancers (think many prostate cancers) are so slow growing they will never kill you, or even disappear on their own. In fact, that's true for approx. 25% of breast cancers. We think of cancer as something that always kills because in the pre-modern technology days, never knew about cancer until it was manifesting serious symptoms. But modern technology allows us to find a lot of cancers that never would kill us in the first place. Unfortunately, once the cancer is found it's impossible to know if it's one of the sorts that is so slow growing you will die of something else before it can kill you, or will go away on its own, or is the deadly type. so all are treated with equal rigor (and imagine, as an HA person, being told you have cancer but you may just want to take the chance of waiting and see if it grows) . So, according to Dr. Welch and many other physicians, our perception of the risk is skewed by virtue of the fact that many of the cancers are non-lethal and not even harmful.